Cassidy was discovered at age 14 by a talent agent in Florida and started modeling and acting in commercials. She got a one year scholarship at the Huntington Film Institute in Orlando, which led to a part in the Nickelodeon series Clarissa Explains It All (1991). She then (1993) moved to Los Angeles together with her mother Amy to start an acting career. Her first on-screen appearance was in the TV show Angel Falls (1993); next she was cast in the short-lived Spelling show Models Inc. (1994).