When Kevin Costner first reached out to Sienna Miller about playing a pioneer in his four-movie, three-decades-in-the-making passion project, Horizon: An American Saga, the actor was flattered. She had been such a fan of Dances With Wolves—Costner’s Oscar-winning 1990 directorial debut—that she’d named her pet rabbits after two of the film’s characters. But the British-bred Miller also wasn’t entirely sure why the iconic actor set his sights on her for his Western franchise.

“It felt so random, but of course if you get a call saying, ‘Kevin Costner wants to talk to you’—I didn’t want to question it too much,” she tells me on Zoom. (In a statement to VF, Costner explains why he cast Miller: “She has obvious natural beauty, but she has a nuance in her roles that I admired and appreciated. She passed the ultimate test for me because she is believable.”)

In the Civil War–era epic, which opens in theaters Friday, Miller plays a young mother who, after uprooting her family and moving out West, loses both her husband and son. But her Frances is a survivor; devastated as she is, she soldiers on.

“There’s a toughness and a resilience” to the character, Miller says. “But I think in that period, when you’ve suffered this unimaginable loss, which was not uncommon, you had one choice: to survive and thrive and move on with your life.”

Miller has proven her own hardiness in contemporary Hollywood. She overcame fame’s worst early-aughts byproducts: voracious paparazzi, phone hacking, and a hideous medical-privacy invasion when she was only 23. At the time, she was dating her Alfie costar Jude Law, who was so movie-star hot that tabloid coverage of the relationship overshadowed and undermined Miller’s nascent career.

“I was very desperate to be taken seriously because I had a huge amount of fame before I’d ever had a film come out,” says Miller, who had made only one mainstream movie before Alfie—2004’s Layer Cake. “It was a constant battle against the perception that I was something frivolous, perhaps, or someone’s girlfriend.”

She proved otherwise by successfully taking Rupert Murdoch’s News Group Newspapers to court twice—the first time before she turned 30. In June 2011, she received a formal apology from its News of the World tabloid, acknowledgment of phone hacking, and damages, helping to precipitate the publication’s shutdown the following month. A decade later, Miller won substantial damages from the publisher after alleging that The Sun pushed her into decisions about a pregnancy, which she ultimately terminated, when the tabloid discovered the news by allegedly illegal means. (As a term of the settlement, NGN did not admit any liability.)

Even so, Miller has spent much of her film career in the lead-actor penalty box, wringing what she can from peripheral parts as wives, girlfriends, and mistresses in Oscar-nominated films like American Sniper and Foxcatcher. When she’s landed leading roles with actual room for range on either stage or screen, she’s earned excellent reviews. See: Tippi Hedren in The Girl; Maggie in Cat on a Hot Tin Roof; Sally Bowles in Cabaret; a blue-collar grandmother grappling with her daughter’s disappearance in American Woman; and a politician’s spurned wife in Anatomy of a Scandal. Though Miller is only one of dozens of characters in Horizon: An American Saga – Chapter 1, her performance as a grieving mother is the emotional standout.

About a month after the first Horizon film premiered to an 11-minute standing ovation at the Cannes Film Festival, Miller logged on to Zoom from a hotel room in Los Angeles, where the youngest of her two daughters was napping. In hushed tones, the actor discussed fulfilling her ’90s dream of working with Costner, surviving early-aughts stardom and scandal, and fighting for more of the types of roles she deserves.

Vanity Fair: I read that on your first Zoom with Kevin, he ended the conversation by telling you that he would show you an American West you’ve only dreamed of.

Sienna Miller: Yes. He said, “Will you go West with me?”

Did he deliver on his promise?

He really did. My whole concept of America had been so New York to LA and a little bit in between, but I’d never really explored the West apart from California. But the middle of Utah [where Horizon was filmed] is the most extraordinary place. Even flying over the Rocky Mountains and imagining that that route was traveled with wagons and children…it was an unfathomable achievement to get across the country.

So when I was in Utah, we drove on the weekends with my [older] daughter, [Marlowe], to this place called Dunton Hot Springs in Colorado. We went skiing in Wyoming. Now I’m obsessed, and I need to go to Yellowstone and Montana.

Horizon is an incredibly ambitious undertaking for Kevin, who put $38 million of his own money into this four-movie franchise he’s been envisioning for decades. What did you initially think, though, when you received these four giant scripts?

I thought it must be a [TV] series, because it’s unheard of to set out to make four films unless it’s Lord of the Rings or Harry Potter. It was obviously original screenplays, and I was very confused because each script was very long. But the writing was incredible. It was almost like reading literature.

And then it’s Kevin Costner. I am a child of the ’90s. Dances With Wolves was genuinely one of my favorite films growing up. So the idea of making a Western with Kevin Costner was a no-brainer, if only to be in his orbit and to absorb this landscape and experience. We basically use natural light, hundreds of extras, horses, wagons, Indigenous people in full regalia. It’s magnificent to see traditionally dressed people and animals in that landscape everywhere you look.

You have a devastating scene in the film in which you say goodbye to your teenage son after he has died. What was it like to film that as a mother, especially considering that you were pregnant while filming the first two Horizon films?

It was such beautiful words. That was the thing about the script. With as much dialogue in this film as there is, it’s probably hard to focus on it—but the words were so beautiful.

The boy that played my son was Kevin’s son Hayes, but unfortunately he’d had to go back to LA. So I had a stunt child in my arms who was much bigger, and mortified that I was holding this ginormous stunt person in a wig that didn’t really fit. I mean, if I looked down, I probably would’ve laughed, but I did cry many times reading that moment in the script. As a mother, all of this stuff is agony.

It’s your worst fear as a mother, and one you’ve confronted before, in American Woman.

I remember with American Woman, I became very uncomfortable with the idea of doing it when it became reality…. When it was like, “We’ve got the money and we’re going to go do it,” I was like, I don’t want to do this. It feels like a horrible space [to explore]. I wonder now, having had my second child, if I would want to. Certainly not at this moment.

There’s something about being a parent where I find myself having intrusive thoughts. Like my elder daughter, when she was little, would look out the window, and my mind would go to her falling on the ground. I’m sure there is a biological, brilliant reason that you are imagining disasters all the time in order to protect your kid. But there was something interesting about going to the worst place imaginable and exploring it, even though that sounds incredibly [masochistic].

You’ve also done it with Anatomy of a Scandal, revisiting the horror of living out a relationship in the public eye.

I’m done with grief and torture. I’m ready for some levity in my work. But as an actor, I do find exploring those shadowy hearts or personal trauma useful and interesting. It’s very interactive therapy, but I think I’ve done it now and am ready to sing and dance and have some fun. And I don’t think my mother particularly can handle any more gut-wrenching performances. I think she said, “Please do a rom-com. I can’t cope.”

It’s satisfying to see you in roles that use the full range of your talent, especially after years of playing characters who were the girlfriend of, the wife of, the mistress of. Do you feel as though you’ve finally been recognized for what you can do as an actor?

I don’t know whether it’s a function of getting older or just not caring as much, but I do feel like I’ve shown that I’m capable of doing things. [When I was young], I was very desperate to be taken seriously. Even if I was doing Shakespeare and West End, which I was, people didn’t want to focus on the work. And that’s probably why I made incredibly intense choices, just to be taken seriously.

Now I do feel like people are aware that I’m capable of good work. I don’t feel as attached to proving anything, which is very liberating.

When you sued News Group, you were not only taking on publications that violated your privacy, but also some of the tabloids whose narratives limited your casting potential for a period of time. Did the court outcomes feel like a full-circle vindication?

It was more for the course correction of what my life narrative had become because of them. It was important for me to stand up for myself in that way. I also am vehemently against the practices of hacking and stalking, and all of that was just so ugly. It felt like there was something that I could do. I mean, going back in and revisiting it [during proceedings] is deeply unpleasant. It’s something that I just don’t think I have the stomach for any longer.

So yes, I think it took real courage to take that on. I do feel a sense of pride. I’d love for none of it to have happened, but it’s an interesting chapter. Even at the time, I think the work I was putting out—I’m really proud of it. But it was just a huge, dominating perception that I felt and I still probably have traces of around.

So you’re able to look back at those early films and appreciate them without the emotional baggage?

Layer Cake was pre-Alfie, and it was just joyful and fun, and a small part but in a really cool cult film. Factory Girl, I gave my heart and soul to. I’m really proud of Interview with Steve Buscemi. I would only make that movie for the rest of my life. I had such an amazing time shooting it. And I did plays.

I think that the work really holds up. I feel confident in it now. There are definitely some duds in there, but that’s because I was just choosing projects to explore things and am not someone who’s particularly strategic about choices.

You also did Curb Your Enthusiasm recently, playing a version of yourself. Do you get offered a nice variety of roles these days?

It feels like a nice mix. Curb Your Enthusiasm was a total curveball. That was great. That made me feel like, Oh, there’s a whole other universe to explore. I would love to be at the place where I was on the list for the top directors in the world and was instantly considered for those things. It’s still challenging. I have friends who really have reached the apex of whatever this is and still feel that yearning. I think that’s part of being an artist in some way—that no matter what, you always feel like there’s higher to go. I feel very fortunate that I’ve worked for 20 years in an industry that is difficult. I have worked with amazing collaborators, but there’s more to mine. I want to get to a different level, for sure.

How much have you paid attention to reviews in your career? Do you avoid them?

They find you. If you’re doing a play, I would not read the reviews, but you’re aware if you’ve got good ones or bad ones. And it’s painful. It’s horrible. You want everything to be incredibly well received. Everybody’s given a lot of heart and soul to creating something, and it’s really fucking hard to make a good film. So I don’t sit in them and it certainly doesn’t dictate decisions, but it sucks if it’s not well received.

Looking forward, you still have two Horizon movies to shoot. What’s the timetable for filming?

Apparently we’re going back in August to shoot until November, and I would be [filming] sort of six weeks in there. But nothing’s firmed up yet.

Do you have any other projects lined up after this, or are you able to enjoy new motherhood a little bit again?

Taking some time off. Heading back into press has been a lot, because my life was a total little bubble for the first four or five months of the year. But I haven’t got anything lined up. I want to be, from this moment forth, very, very strategic about what I do and not work until it’s something that is absolutely the right thing. Partly because I’m ready to see what happens if I shift the narrative in some way or attempt to be on Yorgos Lanthimos’s list, for example. But also I want to be with my kids, and the idea of going to work for something that I am not completely passionate about would be painful.

This interview has been edited and condensed for clarity.