A person who can alter their shape into a form of an animal. Usual shapeshifters can change into only one animal, but sometimes they can change into multiple forms at will. Silver cannot harm shapeshifters, nor can items of religon. The usual animal form is a very large wolf, and shapeshifters usually get mistaken for werewolves.
The difference is in appearance werewolves tend to walk on two feet, shapeshifters walk just like the animal they change into to and that the full moon has no control over their change, only their emotions.
The pain of losing him became so unbareable, that the shapeshifter changed into the wolf so she could try to feel something besides the pain.