Hard to tell from that pic, and she def needs muscling but her hind end looks to lack depth to me from what I can tell. Her hind end also seems a bit straight through the hocks and stifles which is something I always look at if you want to do any jumping or aggressive speed/rodeo stuff with a horse. A client's horse here has a somewhat similar hind end and just had to have a lameness exam done bc his hocks have been funky and he may need to go on joint injections.
From the little I see she looks okay, but I am unimpressed, and slightly concerned with her hind end angles. Muscling will help some, but without more (better) shots it's hard to say exactly how her hocks and stifles stack up under her pelvis and if the apparent steep croup is just muscling or a matter of bone shape / conformation (which is less fix-able and makes a horse more prone to lower-mid back and hip chiro problems). Just my thoughts.