I am against committing violence to kids - even spanking. It's a complete taboo in my country now which I am glad of. Scaring kids, or using violence to punish them, is a horrible way to teach them anything. Maybe you should talk to her therapist about methods you can use to make her realize she can't hit people. Holding her hands work the very moment she's about to do it, but removing the impulse to hit in the first place is the most important.