Mariah Carey (left) and Oprah Winfrey
10/05/2009 at 10:00 AM EDT
arrived at Saturday night's New York Film Festival screening of her movie Precious
adorned with diamonds and a posse of security guards. But away from the glamorous hubbub, she's just a regular girl at heart, say her costars.
"If you're around her enough, 'Mariah' goes away and she's like everyone else," says actress Gabourey Sidibe, who formed a close friendship
with Carey on the set. "She's just a normal girl who talks about normal things like fashion and things like that. She's so nice."
In the film, opening nationally Nov. 6, Carey plays a plain-looking case-worker
. For the role, the songstress, 40,
bared her face in front of the camera free of makeup and donned dowdy outfits.
"I basically told her, 'I want to see the Mariah I see when I'm in your house and we're kickin' it, watching TV and eating popcorn,' " says director Lee Daniels, who also worked with Carey on the movie Tennessee
. "Nothing at all [surprised me about Carey's performance]. I knew she had it in her. "
Based on the novel Push
, the film tells the story of a pregnant, illiterate teen who tries to change her life by enrolling in an alternative school. Oprah Winfrey
was so inspired by the film, she signed on as an executive producer after the shoot was completed.
"She watched it and she went, 'Whoa! This is something very, very special,' " Winfrey's best friend, Gayle King, said at the screening. King, who's now seen Precious
four times, added, "The film is hard, sad and tragic. Oprah's pulling out all the stops she can to make people go see it."