I really really like this image. To me the original is just so close, what I would do is just move her right so her shoulder is almost touching the edge of the frame which extends the black on her left. It gives more negative space and behaves in the rule of thirds a bit better. I really don't like any of the other crops suggested, but my style of head shots is a horizontal with more space. I've actually been toying with the idea of doing a 16:9 ratio headshot shoot in the near future.
I really like the light wrap and fall off on her face, but wish I could see more separation between the sweater and the backdrop, that goes for her hair as well. It just kind of disappears to rapidly for me. Would like more of an outline.
On my monitor it has a bit of a haze to it. I would have upped the contrast just a tiny touch. or brought the black levels deeper and lightened the subject more.
It's a great image, I love it. Her eyes are saying a lot, and thats all you need.
thats kind of what I was thinking. hard to bring out those shadow details from a jpg.