ooh i just saw the age group, thats a lot more serious than younger kids (mine was under 2) as they are a lot more aware of what they are doing, and often much more verbal
The bites sound pretty bad to draw blood and leave bruising.
Id take issue with it, tell them even if your child did do something (not that Im suggesting she did) where is their behaviour management policy - biting is not an appropriate reaction and they should be working with the child's parents.