Take it from me, an experienced Preschool Administrator, biting happens. It's awful. It's emotional, and no one likes it. The most important thing is the caregiver's attitude and response to it.
She definately needs to be on top of it, but the reality is when there are a group of kids together, it's impossible to prevent at times, and cannot always be predicted; although there are certain behaviors that can be precursors.
If you trust your caregiver, and feel she is attentive, and is supportive and is intervening appropriately you will likely have to patiently wait this out. It generally goes away. Be aware however, any child has the propensity to bite. It's a developmental thing.
Talk to your caregiver, and let her manage it. I suggest you google "biting", or "toddler" behavior and read up on biting.
Another thing; today it's biting, next week it might be hitting, or throwing blocks, or numerous other things.
Do keep an eye on it, but understand it's part of child care, and part of growing up. Hang in there.