I agree, so I'm just going to leave it at that so as to not repeat everything said above. I personally would only start jumping my horse at 6 years of age. And if I ever got an OTTB, I would wait at least 2 years before I think about jumping that horse, even if it is already say 8 years old, because an OTTB needs a lot of retraining before it can start with jumping.
If this girl is honestly clueless about the fact that what she is doing is very unwise - such as buying and jumping an OTTB - then I actually feel sorry for her and I am actually angry at the person/people busy teaching her to do this. If she is aware of what she is doing is not smart, but is still doing it, then she is responsible for what happens to her or the horse.