Biting is one of those behaviors that we call "nervous habits." Other such behaviors include playing with one's hair, cracking one's knuckles and even picking one's nose! Nervous habits tend to increase when a child or adult is "nervous" - anxious, tense or upset. They occur out of the person's awareness, subconsciously. One trick is to make the behavior conscious - ask your daughter to become aware that she is biting her nails and then ask her to do it on purpose for a few minutes. Oddly enough, this can cause the brain to reconsider the habit after doing this for a couple of weeks. Also, help your daughter find ways to calm her nerves in a less destructive fashion - introduce her to soothing rituals (warm milk with honey, herbal teas, stretching, bubble baths, listening to calming music and so on). You can even introduce a new habit to her to replace the biting - such as rubbing a worry stone or chewing on gum (since she is using her mouth to relieve her stress). If none of this helps, consider Bach Flower Therapy (see article under "Parenting" on the parenting-advice.net web site), Energy Psychology (can be very helpful with bad habits) or a visit to your local mental health professional for some behavior modification strategies. Good luck!    Sarah Chana