We report on the first successful extraction of a β+ Gamow-Teller strength distribution from a radioactive isotope in an intermediate-energy charge-exchange experiment in inverse kinematics. The (7Li,7Be+γ(429 keV)) reaction at 100A MeV was used to measure Gamow-Teller transition strengths from 34P to states in 34Si. The results show that little mixing occurs between sd and pf shell configurations for the low-lying 0+ and 2+ states even though 34Si neighbors the island of inversion and low-lying 2ℏω intruder states exist. Shell-model calculations in the sdpf model space are consistent with these findings.