I won't touch a rearer with a 40 foot barge pole, and one that nearly flips either goes to live in the paddock, or gets a bullet in its head.
They are DANGEROUS! I know people who have been crippled for life, and killed, by rearers flipping over.
The fact that she is using rearing as an evasion to simply going forward is not good. This is a very big problem and I could never, not in a million years, give you advice on solving it over a forum - I don't want you being injured or killed hanging over my head.
If you REALLY like this horse, and she's super talented in your discipline, then take her to a very good, VERY qualified trainer. See what they think of her.
The issue with trainers though if you send the horse away without being part of the process, is that they may be able to convince her to stop rearing for them, but as soon as you take her home, it's likely that she'll start up again as she knows that she gets away with it with you.
Again, I wouldn't touch her. I value my life too much. Bad horses cost the same to keep as good horses, why risk your life on something so dangerous when there are many good, sane horses out there.