Ouch....we've dealt with this, too.
Taking the baby from the breast will normally make an impression. As you remove her, you can tell her 'no biting!'. This usually worked well for us. It may take a few days, but she should begin to understand that a bite=snack bar closed. :D
I'd get a nursing necklace if you don't have one....I found also that distraction kept Braeden from biting me (until he broke my necklace....*sigh*). And it also kept his hands from mashing and pinching and twiddling (which drives me MAD!).
Good luck!
Amy
Amy
Mom to Holland (9), Madelyn (4) and Braeden (17m)