This being quite obviously a candid photo, making the best of the given situation, it is really pleasing. I do like the sparkling in her eye from the light source (whichever that was).
True fact that remains is that this quickly-using-the-situation photo is kind of flawed by the person behind her. It is less his arm than his neck and t-shirt that bother me, but all in all this could be even better without the person.
You might want to place it into the Photoshop Challenges (a much underestimated sub-forum to the Photo Themes) and have someone try their hands on the background and see what they can do, or your can work on it yourself? Or you just leave it as it is and say: for what I had I feel this came out really nicely.