Did anything I said make any sense?
It's one thing to pick up your baby girl from daycare and find she has been bitten. Its another thing when the teacher tells you that she started it and it took both daycare workers to hold her down/back afterwards.... so is there some kindof 9mo transition no one ever told me about. Why is my baby a punk?
Babies can begin biting because they are teething.My baby bites. What's going on?When Baby Bites
Considering that she is only 9 months old, I'm going to suggest that the "it took both daycare workers to hold her down/back afterwards" is at least a bit of an embellishment on their part.
She may well have bitten the boys first, and they bit her back, but she's only 9 months old and doesn't understand that she hurt them, just that she was hurt, and she's lashing out at the source. Now being that she is aggressive in trying to bite back rather than recoil, it could serve her well as she grows into a young lady, especially if you teach her how to have good aim placing her foot forcefully between the legs of a boy.
My suggestion would be to take her to daycare on a day you don't need to leave her there, and let her mingle and mix as she would normally, and the first sign of her starting to bite someone, intervene and sternly tell her "no"; the only one she is likely to listen to at this young age is mom or dad, though mom generally has more influence.
If that doesn't work or she shows other aggressive behavior, then something else might be at play, or this could be her way of adapting to being separated from her parents for any period of time, or even adapting to other kids; kind of along the same lines as what Paquita said.