How do you get the 'rear' out of a horse?

It sounds like she needs more exercise to me. A horse with excess energy is less likely to keep all four feet on the ground. I would exercise her, ride, longe, chase her around a paddock, I don't care...before you do your halter work. Then if she still can't keep her feet on the ground, discipline her for the specific offense, like you are doing, but then exercise her again. I would probably practice with a longe rope, so that you can immediately send her out for 5 to 10 minutes, then try again. He will get to a point where she understands to avoid that undesirable behavior of rearing, and have much less interest in doing it anyway.