The quality of light in this photo is absolutely remarkable, I don't know how you've pulled it off in such condition! And not even as much grain as I'd expect to be wonderful shot!
This image looks so natural and candid by the look on her face. If I had not seen other pictures of her in your gallery, I would have thought she was a random person. Then again, if she was, I'm sure she wouldn't have wanted you to take this picture...but I could be wrong.