The best thing you can do if you want to keep this horse is get a trainer. I got my horse when she was green and badly trained. Not only that, but I had only been riding for about five months. I believe it would have ended in disaster if I hadn't had a wonderful, knowledgeable horse trainer/riding instructor/boarder that was right there. It has worked out very well for me, but keep in mind this is one of few success stories in these circumstances.
If you choose to keep her please get a trainer working with you, and definitely take a bunch of consistent lessons. It very well might work out in the end if you do. I can only imagine how hard it would be to lose a horse you have been dreaming about for so long, but she will hinder your dreams. You will be worrying about training and behavior problems when you should be enjoying yourself on the trails. I did. It has ended up being worth it for me though.
There also is the option of sending her of to a trustworthy horse trainer for a few months or so. That will make it a million times easier for you to handle her, and she will be so much less of a challenge for you. But still have those lessons.
Please keep us updated and tell us of any progress!
**I must not forget to thank the difficult horses, who made my life miserable, but who were better teachers than the well-behaved school horses who raised no problems.**