While Thiessen's addition to "Beverly Hills 90210" did give it a much needed shot of new life, the show was past its prime and quickly becoming a soap opera rather than a drama. Thiessen, with her stylish new short hair and prominent breast implants, played up the part of the sexy bad girl. Thiessen maintained a level of believable acting, even as the storylines around her became more and more far-fetched. She felt, however, that she was increasingly being used as a sex object on the show, and in 1998, decided to leave and pursue a film career.

Thiessen appeared in two small budget films in 1999, the comedy "Love Stinks" with Bill Bellamy and Bridgette Wilson and the drama "Speedway Junky." She next appeared in the SNL spinoff film "The Ladies Man" (2000) and starred in the straight to video spoof "Shriek If You Know What I Did Last Friday the Thirteenth" (2000). Although Thiessen had made the difficult transition from child actor to successful adult star, she was finding the notoriously difficult switch from TV to film even more challenging. In 2001, she returned to television with recurring spots on "Two Guys, a Girl and a Pizza Place" and "Just Shoot Me." However, 2002 gave Thiessen her biggest film role yet, in Woody Allen's "Hollywood Ending." 2002 also saw her return as a cast member on primetime, reuniting with Bill Bellamy in the Fox Series "Fast Lane."