Pretty horse. Her hip is actually even with her withers. She's not built down-hill, she appears this way because of her weak back due to incorrect training. She is being forced to carry her head in a vertical position causing her to hollow her back which is apparent in the under saddle photo. This horse needs to go back to the VERY basics to learn how to seek the contact of the bit which will therefore build her topline. My guess is she acts nervous because she is in such pain from incorrect training. I would recommend putting her in a regular snaffle bit, give her her head, and ride her bareback as she doesnt have any muscles in her back to hold weight comfortably and a saddle will just cause more pain at this point.