Dropping out of school soon after being randomly discovered by an agent, Mendes appeared in a few made-for-television productions and hammed it up with Will Ferrell and Chris Kattan in A Night at the Roxbury before being cast in a prominent role in Urban Legends: Final Cut. Working against typecasting despite her teen horror resumé, Mendes next took roles in Exit Wounds, Training Day, and All About the Benjamins. Mendes next began work on a children's book titled Crazy Leggs Beshee in which she wanted to introduce art, history, vocabulary, and values to children in a fun and easily comprehendable medium.

In 2003, Mendes' career took off, with the actress taking on large roles in an ecclectic quartet of high-profile films. In 2 Fast 2 Furious she played a customs agent working with Paul Walker to bring down a Miami drug cartel. Out of Time found her reteaming with Training Day costar Denzel Washington. Flexing her comedic chops, Mendes was the love interest of half a pair of conjoined twins in the Farrelly brothers' Stuck on You. And in Once Upon a Time in Mexico she played another government agent, this time opposite Johnny Depp.

2004 saw no signs of Mendes slowing down, with the Cuban-American beauty starring as the ex-girlfriend of Luke Wilson in The Wendell Baker Story, a film Wilson cowrote with brother Owen Wilson and codirected with sibling Andrew Wilson.