I second the why are her hooves weak? You need to have a vet and farrier check her feet. Maybe take X-rays. She may have navicular (a rotated coffin bone,) have had founder / laminitis. Lots of things... If she is just sore or tenderfooted, proper shoeing can solve that. If it is navicular, or some other thing, you don't want this horse.
If her hooves are soft, shoes (at least for a while) will help. Biotin, and other hoof supplements can help. An OTT horse can have perminant foot / bone problems, that can be very expensive, and many times the horse will always be lame.
I would definitely at the very least, have a GOOD farrier check her feet. Also I would have a vet check her. Unless you don't mind having a lame horse, I would not buy her.