Mariah Carey -- I'm Directing A Christmas Movie ... And My Favorite 'Mean Girl' Is In It (PHOTO)

Mariah Carey is directing a Hallmark movie for the holidays starring her favorite character, Gretchen Weiners from "Mean Girls."

Our Mariah people say she started working on "A Christmas Melody" Tuesday and made herself right at home in the director's chair. We're told Mariah had only one request, her favorite actress from her favorite movie star in the flick. Let's be serious ... she had more than one request.

Lacey Chabert, who played Gretchen Weiners in "Mean Girls" was more than happy to take the lead.

Mariah won't appear in the movie but we're told her music is featured throughout. It's unclear if MiMi tapped into directing legend Brett Ratner for advice.