As above, you could do with giving yourself a better platform to start with than what you have. If you have the RAW fix the colours and fill in the shadows. It's better to take the shot into Photoshop a little flat and control your contrast afterwards (I think, anyway!), than take it in overdone and battle with it for the next few hours. Remember you can make multiple developments from the same RAW. If you've found a nice look for her skin but it messes up her hair, develop one for the skin, one for the hair, and just mask them together before you start with the structural stuff. Soft edged brushes are your friend
You may also find you can develop a new section for that shadow to the side of her face and drop that in.
Once you have a good base I recommend to everyone learning the Clone stamp tool first. It's the most basic of cloning tools, and you learn where to sample from without it giving you any unwarranted surprises. Basically, the clone stamp is all your doing. Learn to do it right and you'll find using tools like the Healing brush much, much easier (And more importantly, when you're faced with something the Healing brush can't do, you have your ill clone stamp skillz to fall back on
).
Small skin imperfections can be dealt with using the Clone tool. Almost everything else can be dealt with using some form of dodging and burning. It can be time consuming, but as long as you're not doing it at 2500% you retain texture, and because it's done by your hand and not by the computer, it's organic, and thus looks natural. I don't mean dodging and burning as has been linked above, that's contouring really, just localized contrast adjustments (That's all it ever is technically speaking, but I'm referring to the skin retouching method, not contouring).
Once you've dodged and burned you're usually left with some colour shifts (in skin raising dark shadows will typically leave red areas, whilst burning highlights leaves greyer desaturated areas). If you know how the skin will shift before hand you can clip a Hue/Sat layer to your Dodge curve and correct it as it's happening, though you tend to pick that up with experience. Don't do it for now. Just work out what's doing what and correct afterwards, you'll learn the tools much better.
I wouldn't recommend the frequency separation method linked to above unless you really understand layer structures and the basic ways of doing it first. Sometimes that method can cause more problems than it solves.
E: Paul, just dropped you a message to your Gmail.
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