I suck at portraiture, but here goes with my thoughts:
1. Looks too well lit - look at some of the shadows. I'd use another brolley etc for minor fill in lighting, especially around the mouth, just to soften those shadows a bit. You don't want to totally remove them, just soften them imho.
2. ISO 1600! Yeah gods! Use a tripod, a cable release and mirror lockup. Use ISO 100/200 to keep noise down to acceptable levels. Oh, and run a noise reducer like Neat Image as well after all post production!
3. Exposure looks fine to my eyes
4. You cropped it a bit too tight, you've cut off her hair at the bottom right hand corner of the image. You wouldn't cut off part of her face would you? Don't do it to the hair! Other than that, the pose is fine to my eyes!
5. Leave the background backdrop in the image next time...it does look odd after you've removed it.
Not a bad job at all, I'd certainly be happy with such an effort myself.
As to some others not reading posts thoroughly, I had to laugh. I was about to post exactly the same thing!!!
Cheers,
Dave
edited: Oh, and use something like a 85mm f1.8, it's a very nice lens for portraiture work. I don't have one, so I'd most probably use the 70mm end on my 70-200 f2.8 instead...use the f1.8 or so, rather than f7.1 for a nice bokeh and better shutter speed.