This is my take on it.
first off a better crop. girl on left looks too stooped - looks like she has a hunchback. So crop tighter to get rid of thet.
Then colour balance. I added contrast and desaturated a tiny bit.
Then sharpened and finally a touch of noise removal to soften the skin.
I would take longer and clone the shadows etc but you get the idea.
Oo yes made the background a bit more high key as well - looked a bit grey in the original.
Hope this helps