I'm no horse trainer. But I've had experience with horses throwing their head into the air, I would work from a walk. Play with your hands until she drops her head and immediatly release pressure, to teach her to give to your pressure. Then I would start with a walk only, and work on asking her to stop and keep her head down when you ask. Then after lots of practice she will keep her head low when you ask her to slow or whoah. Everytime I stopped my horse would listen but pop his head up in resistance. So we worked on this, I ignored it for years until a trainer pointed it out, so it took a while to get him to drop his head at a whoah.