S.P.
1) Check with La Leche League.
2) Is she biting not while actively sucking but later on,
after she's already taken in a significant amount of milk?
She's experimenting.
3) When my son -- many many years ago --
would bite when nursing, I would (kinda) YELP
and immediately take him off the breast.
It happened only a couple of times and then never again.
S.