After you have thoroughly checked everything else, and ruled it out (and that includes all tack fit, chiropractic assessment on her, I agree, look to yourself. Are you grabbing at the bit, when you don't have the draw reins are you trying to pull her head in yourself, what type of bit are you using? I don't know you, and I haven't seen you ride, but to me, draw reins, as well as tie downs, and martingales are just devices generally used for a quick fix, and all they do is make a problem go away until you remove said equipment. I would ride her without any of that stuff, and keep very light contact on her mouth and just push her forward, get her to move under herself properly, and see if that helps. I want to make a point here, because I didn't want to interrupt my flow above, but a note on all that added equipment, in the right hands, and used the right way, I do think that they can be an effective training tool, though I'd prefer not to have to use them myself if it can be avoided, so I'm not trying to say that everyone uses them wrong, or that even used the "right" way that its still just a quick fix, but it should not be used IN PLACE of proper training.