The big difference is Open is for horses of any breed or combination that specialize in style over fences at a good pace. AQHA (or any breed restricted Hunter class) is for horses that first are that specific breed and also display style and pace as the breed type and breed specific conformation allow. Styles such as “headset” and pace can be very different between breeds and open too.
No idea how this one would go in either venue, need to see her over a course. AQHA style is very “headset” oriented compared to Open where overall movement is more desirable then head placement. In all these, mares poll is below the withers and nose behind the vertical, she can’t jump from that position and can’t open up her stride from there.
Most of the Artful horses can go well without their nose at their knees and get a decent pace. Like to see this one allowed to go on and see what she can do. Might take a bit to convince her she can go less…oh…“framed” and allowed to open her step. Offhand she looks fairly well balanced, not downhill and should be able to do it.
She also appears to need to muscle up more overall, not more weight just better distributed. Moving more freely with less “frame” should allow her to use herself better and take care of that. So will a little more age, she looks a bit immature. Probably needs a little more time before going into regular training over fences several days a week. Many QH folk like to show them as Junior Horses, horses age not riders. Then breed them or sell them with a record. Sometimes they push a bit too hard to get those Jr Horse points before they age out. Not all, off course, but a consideration when buying young QHs.
Question, is her 1/2 brother out of the same mare? If so, how have her other babies done? If it’s by the same sire, they are just by the same sire. Not considered 1/2 siblings unless out if the same mare. That’s because a stud can produce 40 or more foals every year, the mare just one plus the mare raises the baby giving it her attributes in attitude and willingness to accept training.