He didn't need to know where her head was. If you're shooting at somebody in such a small confined space, who's already down, and you keep shooting, one or more of those shots will be fatal. We've been told that any of the shots that hit her would have been fatal without rapid medical aid, because of the nature of the bullets. He just shot until she stopped screaming.
You're right, but I think it's possibly Viper's post which should've had that reply, because I think steveml was basically saying the same as you (in response to some of Viper's posts)