Kendall hit the nail on the head. The same tactic worked with my daughter quite well. We never hit either of our kids, but I won't deny that tactic to anyone. Some of our friends have made good use of a sharp reminder to the hindquarters, though never on a frequent or prolonged basis. Kids come with very different personalities and learning styles.
I'd be interested, perhaps in another thread, to hear how that child wound up. Sound's like Kendall's wife was giving her the kind of human engagement an abused child needed.