I've completed her chin by drawing a line of shadow under it. This makes it look three-dimentional. The I applied some tones on her chin - voilà.

The parting of the hair turned out pretty well as well. I kept on adding strands of hair, which got thinner getting closer to that part. I then drew in some value to her scalp with a 2B pencil.

You can see my technique I have with hair on her right shoulder. It may look a bit strange, but I always apply the very dark parts first and this is how it looks like.