Hugs! I didn't have a biter, but a hitter. It was so stressful! It came upon suddenly and once it disappeared I thought it was really gone...but no, it came back in full force! I think mostly for him, it was a lack of verbal skills that was the main issue. Since he's been talking more and learning how to communicate the problem has disappeared. Yes, it also could have been age (it was about 18months to just over 2) and him growing out it, and it probably was a combination of both.
I think setting up a meeting with the day care is a great idea. It shows that you are willing to put in the work and try and solve the problem, I really think that's one of the biggest issues. Day cares deal with this a lot and should be willing to be cooperative and understanding.
Other parents will give you the evil eye or deem you a bad parent b/c you can't control your kid, but those people just don't get it. Continue intervening and even using a time out of sorts if she bites when you are around. Ask the school what they suggest and maybe do the same things they do there.
As far as them not watching the kids closely enough, well it's hard. Yes, they should be keeping a closer watch on her given her history, but it happens so fast that they can't do everything at once. I was such a hoverer around my son all the time so I could stop the hitting before it happened, and most of the time I did, but not always, and I was literally right on top of him most of the time...I'm sure other parents thought I was a crazy helicopter mom! ;) But for me that was a one-on-one situation, it's not like that in the classroom.
Hang in there, it will pass. Just keep working on it and I would probably even call your pediatrician again. Also, see if you can find patterns as to when she's doing it like she's angry, she's not being understood, she doesn't want to share, etc. Then you'll have more of a chance to redirect before she bites b/c you'll know what her issue is.