This is a perfect example of how hitting a horse does not work. I would stop smacking her. Horses are not dogs, they don't understand discipline like that. Just my opinion. And I don't think smacking dogs is good....oh gosh you guys know what I'm saying!
Teach her to back up by wiggling your rope. If she is back away from you she can't hit you with her head.
If she goes to do it simply block her with your elbow. If she still insists back her up. Simple, easy solution. None of this smacking business. She will learn that it's just not possible to do this behavior anymore without hitting herself with your elbow. She'll stop. But you will need to be consistant and persistant. Also teach her that she is to stay out of your personal space unless invited in. You can do this in a very easy way, just back her out and go about your business, walk around, pick up brushes, etc. and if she moves put her back where she was. This is actually a fun exercise if you have the right attitude behind it.