Mostly I think that she's learned that if you don't have the reins, she doesn't have to listen. Ask her with legs/seat, whatever you do, just without reins. Maybe let them fall on her neck, but keep a finger or two on them. Sounds like she's pretty light. Ask nicely, and if she doesn't listen, then just use your few fingers on the reins to remind her that you're serious. LOL. Repetition and consistency. Never let her get away with not listening to your legs without a correction. It's worked for me in the sense that when they decide they don't have to listen, you just keep reminding them that they DO, and eventually they'll listen to the leg cues because they know that if they don't, you WILL correct them with the reins, and they're going to have to do it anyway, so why not just do it the first time you ask? Once you can do it with the reins lying on her neck and you can do... say a whole reining pattern, or a whole dressage or jumping course without once touching your reins, then go to a halter, and repeat what you did with the bridle. Then, for me, it's mostly a leap of faith... Take the halter off, and see how it goes. I'm always a little nervous the first time, but usually they don't even consider resisting, because by this time they figure that I'll correct them if they refuse, so they don't even think about it. Since the thought never crosses their mind, I don't get into any trouble. =)
So there's my strategy, hope it helps you. Good luck, and have fun! =)
To rein a horse is not only to guide him,
but also to control his every movement.