Ginger Snaps 2: Unleashed (2004)

It only dies if you do.

Brigitte has escaped the confines of Bailey Downs but she's not alone. Another werewolf is tailing her closely and her sister's specter haunts her. An overdose of Monkshood - the poison that is keeping her transformation at bay - leads to her being incarcerated in a rehabilitation clinic for drug addicts where her only friend is an eccentric young girl by the name of Ghost.