Firstly Id be trying to figure out why all of a sudden she has started biting her nails, ds (soon 6yo) started biting his nail when he started kindy (when he turned 4) and its a nervous thing for him, bites when hes uncomfortable and then talk to her about it
This is exactly why DS was doing it. It was a reaction to the stress of being bullied. We had very strong words with the teacher and Principal with regards to the bullying and managed to remove one of the causes.
We did talk about it and gave him some other ways of dealing with it but in the end we resorted to bribery to encourage him to stop. We told him that for every two days he didn't bite we would buy him a Lego Minifig and if he could get to the end of two weeks we would buy him one of the sets he was after. That, and other coping strategies, seemed to work.
It gave him something to focus on rather than his nails which were really quite sore at one stage.