Sometimes one element in an image can be so "off" that it makes it hard to see anything else. My first reaction to seeing this picture is "What's wrong with her forehead?" When I compared the painting to the original photo, I saw that the model had a very wide, square face, which you narrowed and made a bit rounder. Unfortunately, this makes the forehead look odd.

Sometimes, we look at something for so long, we can no longer see the distortions. For instance, the longer I looked at this painting, the harder it was to see the the distortion that had been so clear on initially viewing the piece.

Here's a trick I use: cover up the forehead with you hand, then fill in the missing piece in your mind. Quickly pull your hand away. Does the actual image match what you imagined?

In addition to the forehead, the left and right halves of her face don't quite seem to match. For instance, her left cheek seems wider than her right.

As I said, it's hard to get beyond the problems with the face. About the only other thing I might suggest is that both the figure and the background are sort of evenly rendered. If you increased the contrast somewhat, the figure would "pop" out more. By "contrast", I mean increasing the differences between the model and the background; for example, you could darken the background or you could give the figure more vivid colors.

I hope you find these suggestions useful.