What have you tried? What type of bit do you use, and do you have a martingale? Another thing you might do, is get a strong man to ride her a few times, and if she can't get her head up, she just might give up...hopefully.
I would first start lounging her on grass, or around open land. I would then work her in a round pen on grass. When you ride her and she bolts, turn her in the tighest circle you can. She will have to slow down. be prepared for a fall, the horse usually slips and falls the first time or two. Also use side reins, and pull her head in tight. You will probably have to work her on a loung line first to get her used to it, and she will probably try to buck. I have used these things alot working with rescued horses. It isn't easy, and takes time. Good luck
I suggest some ground work on some flexing exercises. By doing this you gain a bit more control over the whole body. Teaching to turn on the forehand can really disable a horse trying to either run or even buck. Its pretty hard for a horse to do any of that while he is bent into a pretzel. Keeping their head down helps to hinder them running off but they can buck like a banche with their head down so I have them pivot on the forehand as they cant do either of those things in that position. Its kind of hard to explain and I am trying to remember which trainer I got that tip from. I am thinking it is Dennis Reis or maybe Clinton Anderson and perhaps both and it may have even been the horse training coach in college. I have had this method work in both cases, you just have to do it at the slightest incling the horse is going to do it and do everytime the horse attempts it. Eventually they start trying it a little less and less each time and eventually do good. Your basically knocking him off of his rear and disabling him from any forward movement which is required for either bucking or bolting. Once the horse is standing quietly in a pretzel, you release the rein and your leg and try to resume, he will probably attempt it again pretty quickly but do it again and again. If I come across a trainer who has videos that does this I will post it but I dont know if I will be able to find it. Watching it does a much better job than trying to explain it in a paragraph especially if you dont know alot about the mechanics of how a horse moves, thinks, and reacts.
Ideally you wouldnt usually start a horse under saddle until you are confident most of the squirts have been worked out and an understanding has been accomplished but horses learn bad stuff over the years and they are horses and sometimes just get a good kick out of it. Like humans, they are not perfect. If you really want to get involved, I recomend some lessons from a reputable barn and instructor even if its on one of their horses. You would learn alot about about how to correct your horse at home or just better able to understand why she does it which would have help a bunch.
take this from a 9 year horse trainer/saddle breaker* keep her head about 5-7 inches away from her chest and hold it there and put her into a canter (OUTSIDE!!!) and if she bolts pull her head all the way into her chest until she slows down beware for some falls and wear a helmet the falls can be pretty nasty! and if you fall keep your hands across your chest in an x and keep your head down!
As life goes on, you realize there are things in your life that are one of a kind.You know that its hard to live without them. You gotta be strong and push yourself forward, no matter how far behind.