What a tough situation. Somehow I doubt her parents would be willing to pay for another trainer for this horse. Maybe you could find a reputable trainer who would be willing to work with him and split the profit when he is sold?

Sad as it is, there are just some horses who 'have a loose screw' and will never be safe. I've personally known two (thankfully not my horses - one a mustang and the other a Florida cracker horse)... no matter how much training, how many trainers, how consistent their handling - they were unpredictable from day to day. The ONLY value they have is as a pasture ornament, and sometimes the only certain future they have is if the current owner makes the tough decision to have them put down.

It's impossible to get any idea of what is going on with your horse over the internet - but if you are confident that ALL his groundwork was done properly, and certain that he should know the things he's been taught, he may just be one of those 'rogue' horses.

I'm so sorry about your accident!