When DS1 on his rare occasion, did bite someone I took it VERY seriously! He was removed from the situation and I made a HUGE fuss of the child bitten - which is what happens in a nursery setting. After spending time with the hurt child, I would then turn my attention to DS.
I don't believe in biting back personally - its a bit like "don't hit your brother" whilst smacking the child!
When my kids were bitten/hit/pushed over, they would generally cry for a while then go off and play (staying clear of the child who hurt them) so I haven't any suggestions for you reg: your DD.
Although I'm not saying biting/hitting is acceptable by any means, I do accept it happens when you get a group of children together (bit like bullying at school - would be very wary of a school who proclaims it NEVER happens - it does!!) but I do expect a parent to discipline their child if they've hit/bitten someone and I get very annoyed if they don't!
After all this, DD2 has been bitten at nursery this morning by a 3yo (she's 4.5). Fortunately, she's quite "mouthy!" and shouted at him to stop
Also wanted to say, when DD2 was a toddler, there was a lad same age who constantly bit/hit/pushed over DD. 18 months later DD went off to nursery and I started my job there. One day this lad walked into my room - and allocated to me! He was the softest/well-behaved and delightful child I ever met