Constant, vigilant supervision.
When you start to really watch her, you can see things escalating --and she's still small enough to pick up and hold firmly so she can't do any damage to anyone, including herself-- so you can hold her hand as she takes a backswing, you can press her forehead gently away from whatever she's lunging at to bite (that actually works with adults, too... one single finger on a forehead and they're nearly immobile, which is pretty funny, really!)
3yos, for all their ability to speak and walk around like mini-adults, are still much more toddlers than school-age kids --especially mentally and emotionally. Do not expect a 3yo to be any better at taking orders or remembering rules than an 18mo. In some ways, they're actually not as good at it.
at 1:15 PM on Jan. 25, 2011