her head seems too wide. I don't think the hair should extend back quite so far. I think her neck should probably curve more gradually as well. Overall though, the picture has a lot of things going for it - good shading and minimal color use, mainly.
This is really lovely and a great show of artistic skill! I think adding some darker tones to the hair like you did around the ears would give it depth and make it really outstanding.
Muito bom cara, gosto bastante deste trabalho.