L.C.
All I could think of is, "Who hacked your daughter off?"
In a child this age and when it is uncommon, it seems more like she was super, super angry. For my daughter to bite (same age as your) she would have to be just seething, seeing red mad! I would want to know what on earth happened. Not to excuse her, because that's no good for her, but just to know what the heck went on.
You handled it. Sounds like someone just pushed all her buttons at once. Bet they don't do that again.