Please do not whack her, and do not bite her. This just teaches her that it is okay to bite and hurt others, and makes her afraid of you or your husband. My son also has been a biter, and it has been due to "excitement" and overstimulation. You need to teach her other acceptable outlets for this excitement and overstimulation. Both of my kids have sensory issues, and my son used to bite a LOT. Thank goodness the daycare knew it wasn't an act of aggression. We ended up giving him a plastic tube that he could bite as well as hard, chewy things like tootsie rolls, and eventually sugarless gum. It sounds like your daughter needs to let out her excitement physically. My son knows he shouldn't bite others, and when he doesn't have an alternative, unfortunately, he bites himself and that relieves his need to channel the excitement. He is 7. My son is in OT for sensory processing issues, and his OT has helped us deal with this effectively through the years. Since she is not doing it to get her way or get attention, or to let out anger, then it is not a behavior issue, but probably more neurological or sensory. If you have a good pediatrician, please talk to them and get their advice. I wish your daughter and family luck.