Cracks (2009)

Set in the 1930s in a strict elite United Kingdom boarding school called St Mathilda's, the story centers on a clique of girls who idolize their enigmatic Diving (sport) instructor, Miss G (Eva Green) (in the film, we learn that Miss G had been a student at the same school where she now works and, in fact, may have even continued on at the school after she graduated). Di Radfield (Juno Temple) has a crush on Miss G, and is the firm favourite and ringleader of her group. When a beautiful Spanish people girl named Fiamma Corona (María Valverde) arrives at the school, Miss G's focus is shifted away from the other girls. It becomes a triangle: Miss G gets increasingly obsessed with Fiamma, Fiamma is disturbed by Miss G and also openly disgusted by the teacher's hypocrisies and deceptions, and Di is terribly jealous and makes Fiamma's life hell.