iridehorses: Yes, the horse is ridable, but doesn't know a whole lot. I have worked with them once before for a few hours and the mare is a Dr. Jeykl/Mr. Hyde personality....she will be dominant one moment, yet if you step her just outside her comfort zone she will become very herd sour and unconfident. She likes people and trusts them to a point, but doesn't see them as leader or a place of safety. She is very smart, catches on quickly (if in the right frame of mind) and I see a lot of potential.
The owner is pretty confident. She really wants to learn and is ambitious and is willing to take the time it takes to get a good foundation on the mare so that she can trail ride. That is her ultimate goal, to have a calm, obedient, safe trail riding horse. And to have fun with on the ground, too! She's very excited to start learning and is happy that she doesn't feel like she's giving up on the horse anymore. Apparently things had gotten bad enough that her herd sourness was a real problem where it was almost uncontrollable.