M.D.
I agree with the others that you need to get to the root of why she's biting them so badly (or she may just pick up some other habit even if you break this one).
With that said, one thing you can try is making her fingers and toes unapealling for chewing on...make them taste bad! There is a spray called "Bitter Apple" that is sold primarily at pet stores (it is to prevent dogs fron chewing on things). It is TOTALLY harmless, it just tastes HORRIBLE (it uses bitter herbs that are totally non toxic). Spray it on her fingers and toes for a few days...I'll bet she quits (we used it on my hands when I used to chew my nails).