This is really an amazing image. The way you've captured her in midaction is really excellent. The shading is very well done, everything appears rounded and three-dimensional as well as rather soft in some areas. I also like the metallic gleam on the blades, but my favorite part has got to be her hair. The way it flies around really emphasizes the sense of movement.

I do think a slight background would help--nothing major, maybe just a slight tint to offset the white. This will help the highlights stand out a bit more, rather than washing them out.