Supplements are not going to change the angle of these hocks and corrective shoeing it not going to change the angle either. This horse probably won't make it as a 100 mile endurance horse, but she will probably be fine on some trails. I would hesitate to do a lot of circular ground work if you don't have to to be able to ride her because it might cause undue wear and tear on her joints. I would ride her and enjoy her. Just don't push her to do extremely long rides. If she becomes lame, then you can deal with that then. Your choices are really to keep the horse or to sell her. If she is fun to ride, ride her.