Have you taken her to a vet? I personally have no experience with this, and I hope someone else can chime in with some useful advice. But really, you are right to wonder. That is very strange. Maybe she has a defect?
No matter what it is, I wish you the best of luck in figuring out what's going on with that girl. Though really, if she seems completely healthy aside from this, maybe it isn't negatively effecting her and isn't something you should worry too much about? Well anyways, again, best of luck!