Theiss’s first film role was in 1988’s Little Nikita, but later that year, her big role came in the hit horror movie A Nightmare on Elm Street 4: The Dream Master as Debbie Stevens. Theiss’s best-known TV role is in the 1980s TV series Just the Ten of Us, as Wendy Lubbock, from 1988 to 1990. She also starred in the 1990s TV series Good & Evil, Home Free, and in The Amanda Show from 1999 to 2000.

Theiss has made guest appearances in numerous television shows, including Growing Pains (she played Wendy Lubbock), Blossom, Parker Lewis Can’t Lose, Beverly Hills, 90210, American Dreams, and Cold Squad. She also portrayed the character of Maxie from Maxie’s World in several commercials for the popular doll.

In 2010 Theiss participated in the documentary Never Sleep Again: The Elm Street Legacy discussing her experiences while filming her role in A Nightmare on Elm Street 4: The Dream Master.