Have a vet check him out. If he is physically okay get a written report so you can show it to an interested buyer (they will probably have the horse checked for their own best interests), and put him up for sale. If he does have physical issues then you have to decide how to move forward from there.
Life is to precious both for you and your daughter to take risks. And being afraid is no small issue, and also nothing to be ashamed of.
There are good ones out there. And don't shy away from a horse of mature age as long as they are healthy and sound. They can be a treasure.
Good luck and please keep us posted.
If you ever find yourself in a fair fight, it's because your tactics suck. ~ Marine 1SGT J. Reifinger