She moved to Los Angeles and started writing for the movie industry.

Her early work included contributions to Hardcastle and McCormick, Stingray and Wiseguy.

As producer for Cannell Studios, she worked on The Trials of Rosie O'Neill and Melrose Place.

In 2000, Mendelsohn joined the production of CSI: Crime Scene Investigation and became its show runner and executive producer.

[citation needed] In the fall of 2003, new long-term contracts made Mendelsohn and Ann Donahue "the two highest-paid female writers in television drama.