An American Crime (2007)

Gertrude Baniszewski, a divorced mother of several children, agrees to look after two girls, Sylvia and Jennie, as their parents embark on a carnival trip. Despite the older daughter's behavioral issues, Gertrude channels her own bitterness and frustrations onto the unsuspecting Sylvia. Tragically, she confines the girl in the basement, subjecting her to torture, and even involving her own children in these horrifying acts.