Vulture had an oral history of the movie that they released to coincide with the launch of the show (Rachel Shukert, one of the show's EPs used to write for them), and they mentioned they had a really hard time casting Kristy (Rachel Leigh Cook and Larisa Oleynik both auditioned for Kristy as well as the roles they were cast in, and Oleynik also was considered as Stacey). The show pretty much nailed it, though.
And I gotta take back something. I couldn't really picture Alicia Silverstone as Elizabeth Brewer, because in my mind she was the perfect scatter-brained Sharon Spier. Boy was I wrong.