my first thought would be to teach her to stand still when she gets scared instead of freaking out, sounds impossible I know, but my horse has almost got it down pat lol
Start with just a halter on her or if you feel you have more control then a bridle, get something that moves like a dishcloth or a peice of fabric and tie it to a stick or even a lounge whip. Kind of wave it at her and if she moves keep the flag(we'll call it a flag) the same distance from her, the second she stops moving and is relaxed take the flag away and reward her. Don't try to hold her close to you or she will feel trapped so let your lead rope or whatever out and step towards her if she moves backwards or to the side. Eventually you will be able to get the flag in front of her face and she shouldnt move at all until you take the flag away then you reward her, you have to be really fast, the second they relax reward, then give it a minute and try again, when she starts to relax faster get closer to her with the flag. Don't start to close to her, I would suggest where she starts to tense and eye the flag or dance around. When she masters the flag move to a can full of something noisey, just increase the intensity as you go, I would suggest you do this until you think she can handle you on her back,
While you arent doing this get her used to you like the user above me suggested, give her love and attention
Im not saying this is the best thing for you to do but it worked with my horse and my neighbors horse, I know every horse is different but its worth a try,
This could also end up kind of ugly so please be careful!!!!!!
And good luck!!!!!!!!!!!
Our horses know our secrets; we braid our tears into their manes and whisper our hopes into their ears.
Truly War Paint-Arabian,QH,TB,Paint,Barb-Diablo