Petty had made her film bow in a 1988 short, "...They Haven't Seen This..." and her feature debut in a small role in the comedy "Cadillac Man" (1990). After the demise of the TV show "Booker" and her hit in "Point Break", she was cast as Geena Davis' younger sister, trying to break out from under her sibling's shadow, in Penny Marshall's "A League of Their Own" (1992). Feisty and funny, she was one of the high points in the enjoyable ensemble film. But Petty found it hard to get a role showcasing her particular talents: after a cameo in the film-within-a-film in John Singleton's "Poetic Justice", she played the sympathetic animal trainer in the children's hit "Free Willy" (both 1993). From a whale to the "weasel", she co-starred with Pauly Shore in "In the Army Now" (1994), as the only female recruit in his unit.
Trying to become an action heroine, she co-starred opposite Sylvester Stallone in "Demolition Man" (1993), but conflicts between producer Joel Silver and Petty over the character's direction were resolved with her part being recast with Sandra Bullock. Petty did get to play a cop, the lone female, in the thriller "The Glass Shield" (1994), then received another career-boosting chance when she replaced Emily Lloyd as the "Mad Maxine" star of the post-apocalyptic action film, "Tank Girl" (1995), based on the Dark Horse comic of the same name. The bizarre, over-the-top film got mixed reviews, but Petty, with her close-cropped hair, was certainly memorable. She briefly returned to TV in 1994, voicing athlete Babe Didrikson Zaharias in TBS's documentary "A Century of Women". Petty co-created and co-starred (with Karyn Parsons) the short-lived 1996 Fox sitcom "Lush Life".