I was thinking of it from the other way around. Tera is supposedly just a wolf. And as a wolf she made the decision to present herself as a human. She also apparently could understand and speak a human language. I guess I'm assuming that her being able to function as a human means that she was capable of human level thought as a wolf.
Though there is evidence that wolves are crazy intelligent.
Crazy. So for me it's not that much of a stretch. And remember that her functioning in society was limited to doing very wolfish things: tracking, managing a pack, running through the woods, et c..