L.C.
Morning J.,
I definitely must suggest discussing this with your Pediatrician if you haven't already. The two usual reasons for nailbiting tend to be nervousness or anxiety and anemia. Even when adults and children are eating as healthily as possible some people do not absorb iron into their systems well or aren't getting enough. You may want to have the Dr. check your daughters iron levels in her blood. Even if she tests within the normal range and does not have anemia, if she is on the low end, her body probably needs more.
I would suggest introducing spinach and broccili into her diet if you haven't already. Another option if you are already doing this is to give your daughter Juice Plus. If you haven't heard of this, you can check out pathasjp.com for more information. It is fruits and veggies dehydrated into capsules for adults, chewables for children and gummies for little ones. I give my sons the gummies and they absolutely love them. They are healthy, have better bowel movements, have energy that isn't unnatural coming from sugar, etc.
I am the anemic one and I take Juice Plus myself. The benefits from having more fruits and vegetables in my diet from the capsules has regenerated by body. I don't crave junk food, I rarely eat fast food, and most of the time my body wants healthier foods that I was traditionally not eating.
Good luck J.! :)