Here is a quick little paint-over (emphasis on the quick):

The two big things that are making her look weird is the location of her vagina relative to her ass and the extreme length of the ribcage. The other thing these guys are commenting about is the fact that the left side of her hip is confused with the stomach on your current sprite, though, I'll be honest I don't know how you would work that in there and still have the legs animate the same way.
The slant between the bottom of the buttcheek and the top of the vulva is way too steep, it should be nearly horizontal. Actually, on a real woman you wouldn't be able to see the vagina from this pose at all, but if you make the bottom of the pelvis jut forward more than usual it makes it look alright (I don't know if I did this effectively in my draw-over).
As for the ribcage, it's just too large relative to the pelvis. In general you're going to want the distance from the clavicle to the bottom of the ribcage to be close to the distance between the ribcage and the bottom of the crotch. Also her belly button is too high

Other general issues: you could probably animate the arm more naturally with a circular shoulder. Also her thighs are curved a bit too much on the top relative to the bottom.