Not sure that it will help you but my daughter has a stock horse mare that was a little similar, i.e. if you put her over a jump, she was likely to land and turn into a saddle bronc as she did land. Diagnosed her to be having trouble ovulating, and in her case, a staple in her ear on an accupressure point did the trick. Talk to your vet as it was ours that suggested it, only cost $70 approx and that staple is still there and working even though it must nearly be 5 years since it was put in.