I bit my nails all my life and the only thing that has stopoped me from biting them is a product from www.whatshebuys.com. I think you have to buy 2 bottles, but I leave one here at work and the other at home. It's super nasty tasting and unlike the other types of nail polish out there, doesn't wash off. I apply a coat of nail polish on my nails and then do a coat of Mavala Stop (item number mav-90312-nb)
I borrowed a bottle to my girlfriend whose college daughter always bit her nails too and she just called me last week and said her daughter finally has long nails. The hardest thing about having it on your nails is to remember not to lick your fingers or put your fingers in your mouth (like when you are eating chips or nuts). You should tell your daughter that you are applying it and it will taste bad. We used it on my 2 year old daughter (she sucks her tumb) and forgot to use nail polish remover and when she put her thumb in her mouth, she immediately threw up (yeah, it's that bad).