The Devil's Arithmetic.

An American-born Jewish adolescent, Hannah Stern, is uninterested in the culture, faith and customs of her relatives. However, she begins to revaluate her heritage when she has a supernatural experience that transports her back to a Nazi death camp in 1941. There she meets a young girl named Rivkah, a fellow captive in the camp. As Rivkah and Hannah struggle to survive in the face of daily atrocities, they form an unbreakable bond.