It's a wonderful painting! Having that said I think it can benefit from some lighting clarification. Right now she looks like she's under water. If you're going for the ambient soft light sort of look, you can still group the lights and the darks into big passages first before breaking them down, whilst maintaining the hiarachy. How do you find painting oil on paper? I usually find it very absorbent and after a short while the colors would start to lose their chroma. Your colors look wonderfully rich tho. Also I think it would help if you include dimensions for your future posts.

I think the head is too small in comparison with the body and the arm.

only thing i would touch up a bit is the left side of the wall. darkening it a bit more would draw the focus more on her and kinda "frame" her. i am not sure about the scene itself, if its supposed to be windows and a city outside but maybe some soft highlights from it might add a bit of a "cut" to the background for her to pop out even more.