This may seem a little weird but to let get her to let go when she clamps down smoosh your boob into her face so she has to open her mouth to breathe. It happens really quickly and then you don't lose a nipple trying to pry it out of her mouth!
If she bites say "all done" and put her down. No matter what you don't want to react (if you want to keep on nursing). If you react it could send the wrong message about nursing, like you don't like it, it hurts, etc. My son did this and I did the boob smoosh and then would say "no biting, we are all done" and he got the hint!
One other thing, does she bite at the beginning or is she bored and just playing? My son used to bite when he was done and bored. Good luck!