I restored a damaged photo once that was no where as tough as your project. The only thing I can suggest is to maybe try and highlight the hair along the edge where the light source is aiming at to give it a more natural look. Not sure how you would do that...maybe a slight touch of dodging(?) Regardless of whether you try that, I'm sure your friend would be ecstatic with the results you have already achieved. I am more than impressed! :)