Ouch! I've got 4, breastfed all of them until they were 3 (or thereabouts, except the youngest, 21 months whose still nursing), and they have all bitten at least once. My youngest was the worst, though! When he was first getting his teeth, he would practice on me, and hey, it hurts -- those little teeth are sharp, and combine that with those strong little jaws...
But, happily, it is usually just a phase, about 11-13 months is the worst part of it, it seems, in my experience, though every little one is different and is not above doing it before or after that -- 2 of my newborns bit before they even had teeth, and it hurt then, too!
Anyway, La Leche League is great, and can offer lots of support and information and tips.
Also, the little ones don't bite when they are actively nursing. It is usually only at the end of a feeding or when they are ready to play with it that they bite.
When she bites, you can try pulling her in to your breast (like hugging her nice and tight really quick while you are nursing - when she bites) and let her know it hurts (for example, "Ouch! that hurts, you have to be gentle with Mama!") It does block her air, like plugging the nose, so she will naturally immediately let go (try plugging your nose - your natural reaction/reflex is to open your mouth).
You could also end the session when she bites (use your finger to break the suction) - don't give her back the breast right away. Just get up and go do something else, or pick up a book and read with her, but not let her nurse right away.
Doing both and being consistent, and emphasizing gentleness, finally did the trick for us, and my little one does not bite me anymore, though he teases me and acts like he is going to while he looks at me and laughs! :) But, he knows Mama won't let him hurt her, so he is learning to be gentle with her.
Good luck, it will get better...