I wouldn't be concerned about the neck reining thing. I got a project in several months ago. A 12 year old western trail horse who neck reins like a dream whose new owners want to learn to jump. I'm sure he was trained to direct rein at first too, but it's been years since he's been ridden that way, or with any kind of contact at all. He absolutely hated it if you touched his mouth at all (got his teeth done, tried different bits, it was purely a training issue). Several months down the road he's finally direct reining quite well and goes on a bit fairly decently. If you don't mind neck reining I wouldn't be concerned if he doesn't direct rein. If you're looking to direct rein you may need to find a good trainer to give him a refresher course.
I'm kind of confused about the giant knots on her side. Did she get kicked? What happened there? It's been a few YEARS??? And what about the shot??
Is she willing to let you bring the horse home on a trial? I'd see if you can do that. It'll give you a place to try her that's a little more ridable and you'll get to see how she is in new places. And get a little more used to her. If she doesn't allow for that I'd try her at least a few more times at the lady's place before making a decision.
And the knotts...Do they sound like tumors to you? Or are they just masses of scar tissue? The one on her side she said the vet stitched up..but if the vey stitched up, how come it's so HUGE?