She's absolutely beautiful!! I really like her neck and wide chest... she is quite a tubby mare right now, but I agree, when she slims down she should be quite athletic... she already is!! She has nice form over the fence, although she is "wonky" through the line. She was disunited in the canter a few times, so you'd have to work on that, but it's nothing a bit of practice and fitness can't fix. Like you said, she's very green. The only thing I noticed is that her hind legs seem to slant inwards when you are looking at her from the back. I can't remember what that's called, but it does mean that when you are turning circles, tight turns etc., she might clip her hind feet together. Putting fetlock boots, or other protective boots on her hind legs would be a good idea. Personally, though, I wouldn't worry about that too much... the positives way outweigh the negatives!! I say go for it... if she's nice (for a green horse) under saddle, has a nice temperament and you "feel" that it's right, I think you should definitely buy her!! Oh, and I think she could go way higher than 2'6"... she has a lovely bouncy jump, and tucks her legs very nicely despite the fact that it was only a crossrail.
Hope that helped! Let us know if you decide to buy her!! :)