I don't see butt-high; I see long, weak back/loin. Cute head and neck Shoulder is a bit upright for a stock horse so she probably has a more upward, round movement in the front. Her hip is nice. Can't tell about her legs much but they seem a bit off - would need better pictures to know for sure.
She is cute overall. I would work her over ground poles, cavaletties, and/or on the trail to get her back built up, as well as lots and lots of backing up purposefully.
I have said what I have said. I have not said what I have not said.