Rose took on some dark magic ... it resides within her.
Rose is no ordinary girl. She has once found dark magic that formed a seperate personality within her. All the time she is aware of what is going on when the demon takes control, but is powerless to do nothing about it. The demon shows itself by turning her hair and eyes completely black, her canine teeth extending to the size of a wolf's, and her voice deepening. The most terrifying part is that Rose can still make herself heard even under control of the demon within her. She has killed many through the demon's actions, which is why she was sent to this camp.