Study of a woman's back

One thing I might rconsider is letting the lines that are on the side of the shadow stay as dark as you have them and the ones that are more towards the light, a little lighter tso that the drawing does not just feel like an outline of the model's figure.

I myself am also struggling with feet, but find that if I don't understand how to draw a thing from a certain angle, I'll try to draw simple shapes I do understand that make up the shape as a place to start.

Nice back view. I hold that backs are interesting. You have done so. I would have made the feet a little bigger, (normal length is 1 head). The feet look just fine. The hands look just fine. You need to do some more. You are coming along nicely.