In Her Skin(2009)

15-year-old Rachel Barber is the perfect girl. A dancer, a beauty, a free spirit; she exudes grace and charm. She is the envy of all girls, especially her childhood friend Caroline Robertson. Caroline is filled with so much self-hatred that she becomes utterly dangerous to herself and those around her. She is intent on becoming someone new. Even if it means murder. One night when Rachel does not return home from dance class, her parents immediately know that something is very wrong. They start a desperate search for their daughter and with the help of the police, piece together the frightening last hours of their daughter's life.