Wicked Witch of the Night

Hermione thought Malfoy was talking nonsense as usual when he said there was a curse on her that would change her into a wicked witch at night. But then to her horror she actually does become a frightening wicked witch the next night, who seeks revenge on all those she had secretly held a grudge against. Is Hermione cursed? Can she break the curse? Sixth year, canon compliant.