I'm editing an outdoor group photo for a friend and one of the people in the photo has a shadow across their face that I'd like to remove or at least diminish. The area of the face in the image is around 300 by 400 pixels. The face is fairly bright and the shadow is from a child sitting on their lap, so the line between regions is quite crisp. Complicating things a bit is that the source is a jpeg with a lot of compression artifacts. I realize it would probably be helpful to see the photo in question, but I'd prefer not to post it since it isn't mine. I can, however, provide additional information if needed.
I created a selection of the shadowed area and then tried some basic adjustments in the levels and curves panels. With these I can get the brightness to almost match the rest of the face, but the color of the region looks quite off. I also tried using the clone stamp with a low opacity and tried to paint over the shadowed area using the brighter part of the face, but I couldn't really get it to look very convincing.
What would be the best way to go about trying to remove or diminish the shadow?
Edit: I got permission to post the photo, but it was too large so I've cropped it down to the part I am trying to edit.