I love the background. However I have to agree with others in the comments: Her ribcage is too small on the way down and with a pose like that it should be sticking out more also the way her head is attached to her neck seems to be a bit weird.
There's something wrong with her right shoulder and her breast Oo' It looks like her boobs are at the same "place" they would be if she standed "straight". Her boobs are way too low and have to follow a paralel line to the shoulder. The ribcage is a bit small and the angle of the back should be in the middle. Dunno if I'm clear. Much simplier with a drawing ><'
By the way, love the way you coloured the skin. Just awesome, man... It's my weakness ><