She made her feature film debut at age 15 in Terrence Malick's period drama Days of Heaven (1978), playing an adolescent girl growing up in rural Texas in 1916.

Manz earned critical acclaim for her portrayal of a troubled teenage girl from a dysfunctional family in Dennis Hopper's drama film Out of the Blue (1980).

While she was at an academy for show business, a teacher told her that casting director Barbara L. Claman was looking for streetwise kids to appear in a new Hollywood film.

She plays a streetwise orphan who joins her older brother and his lover when they flee Chicago in 1916, and find work, then refuge, with a wealthy Texas farmer.

"[7] Manz appeared alongside Ken Wahl, Karen Allen and Erland Van Lidth de Jeude in the 1979 teenage-gang drama The Wanderers, directed by Philip Kaufman,[8] Her next role was in the short-lived CBS series, Dorothy.

[12] In 1981, she starred opposite Leif Garrett and Ralph Seymour in the television film Longshot, which focused on a group of teenage foosball enthusiasts.

Manz insisted this was not due to any dramatic walking-out-on-Hollywood story, telling Time Out in 1997: "There was a whole bunch of new young actors out there, and I was kind of getting lost in the shuffle, so I laid back and had three kids.

[2][9] Manz followed this with the small role of the roommate of Deborah Kara Unger's character Christine in David Fincher's thriller film The Game (1997), the last time she appeared on the screen.