I would be very suspicious of this ad. "Cross country prospect" What the heck is that? It's either an event prospect, or a trail horse - there's no such thing as a cross coutnry prospect. Then - "Has been exposed to jumps once" What?????? You've "exposed" it to jumps once, but you're sure it will do well show jumping and eventing?
I would assume these owners got the horse off the track, found reschooling her was more than they bargained for, and are now looking to lease or sell.
All that aside, she is a nicely conformed, athletic mare, and I definitely see TB. Her most obvious flaw is that her neck is a tad short and also underdeveloped. (Typical in an OTTB)
I don't know what prices are in your area, but I would assume that very little has been done with her since the track and that her price should reflect that.