M.G.
I am going through this right now with my 9 month old son. Check out this link. Kellymom has some suggestions and reasons for biting. The more I react to my son the more he does it because he thinks it is funny. What she suggests is either pushing the baby closer to the breast or breaking the latch just before you see her go to bite and put her down for a bit.
Here is the link: http://www.kellymom.com/bf/older-baby/biting.html