M.L.
Nail biting is a very difficult habit to break, so be kind and gentle with her while you attempt to help her stop. As a nail biter myself, I knew that as I was growing up, my mother would yell at me or nag me to stop, which only made me feel like I couldn't accomplish anything. Nail biting can go deeper too. Most kids whoo bite their nails are nervous or shy and it is a way that they can cope with things.
As far as trying to sop the occurance....try bandaids, lemon juice, the bitter polishes or cotton gloves.
Good luck
M.