The Alpha Assassin

The Alpha's daughter of a rival pack, the last living pack member of the Blood Moon pack was taken by The Black River Alpha and was going to be forced to be mated to one of his three sons when she turned 18 to use her strong bloodline for heirs. There starts to be random disappearances and then people start turning up dead. No one has any clues or ideas of who is doing it. No one suspects that the weak, scared, timid girl was actually a trained assassin since birth, and she is out for revenge.