Ginger Snaps(2001)

They don't call it the curse for nothing.

The story of two outcast sisters, Ginger and Brigitte, in the mindless suburban town of Bailey Downs. On the night of Ginger's first period, she is savagely attacked by a wild creature. Ginger's wounds miraculously heal but something is not quite right. Now Brigitte must save her sister and save herself.