I remember the biting. It really does ruin the whole tender moment, and makes it impossible to relax during nursing. It is like shock treatment- you never know when the next zap is going to come!
What you could to do is refuse to nurse her after she starts biting. Usually when the biting starts during a nursing session, the hunger is taken care of and now they are just chomping on you. If dd was really hungry, she would not be focusing on biting you, so chances are that she has had her fill. If you think she is still hungry for some reason, try again in a few minutes. Tell her *ow, that hurts momma - gentle - no biting* Don't give a huge yelp(I know it is hard not to) because that reaction may be too entertaining!!!
If you are really comitted to nursing(and it seems as if you are) then you know that there is more to it than just the emotional wonderfulness. You know that the nutrition is just as important especially the first year.....so if you stick it out, and keep reinforcing that you do not like the biting(by pulling her off and giving it a rest)eventually she will get it. Biting will be of no benefit to her if it ends the nursing session.
At 21 months I can honestly say that I have those tender nursing moments with dd every day, and I would have missed out on the amazing dynamics of our relationship the way it is now, had I given up when she was biting me so much. It will stop. It is not a fun time, but if you are truly committed to the extended nursing, you can both get through it. The rewards are immense.
ALso, forgot to add, when the biting starts during your nursing session, you can pull her off and hand her something to teethe on. Tell her*you may bite THIS, not momma* She WILL get it at some point. So if she is teething and just needs to chomp, you will see her happily go to town on the teether and not you!
Good luck, be patient, hope this helps you.