I see a decent shoulder, good straight front legs and good bone. I like her big flat knees. She also has a very cute face :)... not that it will affect her performance.
On the downside, she looks quite butthigh in the second picture, however it seems to even out in the third. Her hind end looks quite straight to me, and her hind legs camped under. However, this could just be due to how she is standing and the uneven ground... a different, level picture with her standing square would be great.
She definitely is in need of some extra groceries, and muscling all over. Sorry I don't know anything about barrel racing requirements.