That sounds like a good cross...both arabs and appys are usually very good jumpers. If she is uphill she should jump very well...I just need to see a pic with the saddle off. If she vets clean I think you are getting a great deal on her. I still can't tell for sure if she is bench-kneed...Her conformation is great otherwise, though, except that she is pretty straight in her shoulder, which will make for a pretty short, choppy stride. That won't affect her jumping ability much (I sometimes ride my friend's Morgan/TB mare, who also has a straight shoulder but is an incredible jumper--clears 3'6" no problem), but again can cause stress on her legs later if she is worked hard, and her gaits won't be as comfortable. She has a good-sized head with a kind expression (with maybe a hint of stubbornness), a well-placed neck, strong shoulders, a deep girth, pretty straight legs (except for the possible bench-knees) and excellent hindquarters. If you can get some good pics with the saddle off, I can really tell you whether or not she'll likely make a good jumper...just make sure she's standing fairly square on level ground. :)
Oh, and I think horseluver250 is right about the saddle...I'm an event rider, but it does look too far forward to me also, based on what I know about english saddle-fitting.
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