A friend of mine just went through this same thing. She talked to the director and they said that they were “shadowing” the little girl— they assigned one staff member to follow her around, and when she tried to bite, they’d pull her away, get close to her face and tell her "no." Apparently, they didn't have any luck with this, so they finally expelled the girl. Before that happened, my friend was ready to talk to other parents-- if her little one was getting bitten, surely other kids were, too. She planned to join forces with other parents and demand that they take action-- otherwise, they would all walk. It was a great idea-- I'm sure the daycare would prefer getting rid of one problem child, vs. losing several. Also, a good point you may want to make to the daycare-- in addition to bullying the other children (and teaching them that it is acceptable behavior), you've also got a health issue-- the child that bit my friend's son would sometimes bite so hard, she'd break the skin-- which is a risk for diseases and infection.
Another possibility— we put my daughter in a Montessori school. It honestly didn’t cost that much more than the daycare she’d been in. They were much more structured and the kids actually learned a lot, vs. running around and getting into mischief. Montessori schools are really wonderful places— each child learns at his own pace and is able to pick out activities that he is interested in. They make the learning really fun— it’s like the kids don’t even realize they are learning. Also, they typically put some younger and some older kids in a class together. The older kids have a chance to help out the younger ones— which just reinforces what they’ve learned. We didn’t put my daughter in one until she was around 3, but I wish we had put her in much earlier. I had a friend tell me that in her room, babies would crawl up to a sink (that was near the floor) and wash their hands— pretty amazing!
Good luck! Thankfully, I never had this issue with my daughter. I can’t imagine how frustrating it must be.