1. Waist line is too high in my opinion
2. She has two right feet
I think that ass will click into place once you fix 1.
EDIT So it doesn't be that I am just talking here is what I had in mind (just a quick mock up in Photoshop, I suck at drawing btw):
- model2a.jpg (77.04 KiB) Viewed 2532 times
Now the waist and ass on the left pose look much better IMO, but the legs are too thick and should be thinned down to keep the proportions. Also, hips area is too high, should be reduced a bit.
Note that I didn't edit the second pose (on the right), you should be able to get the idea how to fix it from the first pose.