And a couple of things about the original shot that will save you the headaches you are working through. The pattern of the leaves casting shade (ie, "dappled shade") is just a recipe for headaches - very high contrast stripes across the subject are nearly impossible to deal with without affecting the skin tones, etc. In this case they fall right across the face, making them even more distracting (in my opinion, for what that is worth). It may have been just a matter of moving the subject a few inches to get the face in uniform shade and avoid this.
Second, a reflector or flash is the ticket to this shot to help balance the very bright directional lighting from above, camera right. You are essentially trying to accomplish in post what fill flash would have done in camera with the proper exposure. In this case, you probably wouldn't have even needed a flash unit - just a white, or light neutral sheet or some sort of reflector, placed out of frame camera left to bounce some of that bright sun light onto the model and lift some of the shadows created by the bright directional light.
Also, next time consider shooting in portrait orientation so you don't cut the model's feet and fingers off.
Keep at this one. If you are going to shoot again in this location, consider turning the model so her back is facing more toward what is now camera right - this way you will get the sun to give you nice rim lighting to separate her dark hair from the nice deep background - then you can use flash or reflectors to fill the model's face/body. You can add some modeling to her features by reflecting the light slightly across her, or try straight on as well. Experiment and have fun!
Kirk
.
