My daughter, now 25, bit her nails to bleeding constantly as a child. She has continued to do it into adulthood. She has now ruined her nail beds and her fingers look pitiful. She used to constantly wear Band-Aids on her fingers so people couldn't see what she'd done to herself. I took her to counseling and that didn't help. I would buy the nail polish and creams that taste awful, and that didn't help. When she got old enough to work, she started getting acrylic nails done. The time and money it cost her to do this seemed to be somewhat of a deterrent and she quit biting for awhile. She can no longer afford it, so the nails are off and she's back to biting. I hope you can find a cure for your child, because this is a real problem.
And then...I met the nicest man about 2 1/2 years ago. He is now my fiance'. He is also a nail biter. He bites the skin around his nails just like my daughter does. From what I have noticed, both of them do it when thinking about or talking about anything which is out of their control. My fiance worries (somewhat needlessly) about finances ALL the time. He is consumed with where the money goes. His fingers are in his mouth the minute he starts thinking about this. My daughter is an actress in Hollywood. She is constantly auditioning and worrying about money also. There is so much stress associated with her line of work, and her fingers show it. She and I always say she will never work as a "hand model". If and when she lands a big movie, she will need a hand stand-in for those close-up shots.
Good luck with this. I know it's a real problem. We have tried everything to no avail. I don't mean to be so negative, but this has been my reality. Let us know what you decided to do!