Another Cinderella Story (2008) on Netflix

Plot summary

Mary Santiago, a high school senior who wants to become a dancer, is treated as a servant by her guardian, the former pop star Dominique Blatt, and by Dominique's daughters Britt and Bree, who also bully her at school along with Natalia. Mary's closest friend is Tami. Pop singer Joey Parker comes back to finish his senior year, bringing his friend Dustin, and announces a contest whose winner will dance beside him in a music video. Natalia, Joey's ex-girlfriend, is set on winning him back. Hidden behind a one-way mirror, Mary copies Joey's moves during a class he teaches. Tami supplies a cleaning crew, a dress and a mask so Mary can attend the school's Valentine's masquerade ball, where Joey asks her to dance. She leaves early to beat her curfew, dropping her Zune on the way out.