i shall watch this with interest. DD is 6 and has always bitten her nails (toenails too!). I have tried to do a 'mummy/daughter time' when I trim/file my nails and do the same for her, so she does not think she has to bite them as they are too long. But whenever i come to do it, there is not enough nail to groom!
She had an infection in her finger very recently, due to biting the 'quick' after biting some nail off first. It became pussy, red (and yellow, and brown eventually) and swollen, and very, very sore. She lost the nail completely. It has grown back again fine, but for a good couple of weeks her finger was very very painful. GP saw it as it was healing and said it was ok, but if it had taken a day or two longer, would have needed antibiotics.
I thought that would have been enough to deter her, but despite this happening as a direct consequence of nail biting, she continues.
I am less bothered about the physical appearance. I have horrible looking nails myself, not sure if that is because I am/was a nail biter, or i am a nail biter because I have shit nails. I am concerned that she will get re-ocurring infections because of it.
So I shall see if there is a technique to be used that would help us too !