Find yourself a trainer to ride her. I HATE rearers, actually I detest them. They are so incredibly dangerous, particularly if the cause seems to be 'random'. People die because of horses rearing, flipping over backwards and landing on them. I knew of a lady locally who was riding her horse on the road in a western saddle, the horse spooked, reared and flipped over backwards, landing on the lady and the saddle horn went through her chest and killed her.
If you fall off backwards on a rear, you are going to fall behind the horses back legs and have a **** good risk of copping one hell of a kick.
Get a trainer, if you're not experienced with dealing with this, do NOT persist, find someone who can do it. To be honest, I'd rather dog a horse that rears than risk having the mongrel go up on me. Bucking, spooking, spinning etc. does not scare me, I make my money out of training horses, but I will not touch a rearer.