The main thing that's wrong is that the lips are out of perspective. They're drawn more like they're facing towards the viewer, whereas they should be pointing more away, off to the right.
The shape of lips in perspective is actually kinda complicated. See the section Minor Planes in Proko's How to Draw Lips tutorial for an exaggerated version, showing and explaining overlap (and the rest of the tutorial for a better sense of lips in general).
There's also some odd shadows that e.g. indicate indentation when I'm guessing there isn't any (between the eyebrows/upper part of nose -- reads a little more like dirt because you use black to make that shadow), which suggests you're not super familiar with facial structure (like planes of the face, Reilly method, facial anatomy and perspective, etc.), so that might be worth studying up on.
Even if you're just copying a reference photo, it's still useful to have a good understanding of the structure you're copying. Makes it faster to see and use the information in the reference photo, especially if some part of the photo is unclear or distorted.
Plus, building up a drawing from a reference photo like you would do it for an imaginative drawing (i.e. structurally) I'd guess is good practise (depending what you want to practise).
I redid the portrait, this time paying closer attention to the values as well as the overall structure of the face. Though I found the Reilly method to be quite useful for getting the structure down I still had far too much difficulty simplifying the face into basic forms.
Yeah. I spent quite a bit of time on that portrait but I was only making it worse and worse until I finally gave up. I really need to work on my understanding of the structure of the face. Do you know of any good websites with reference images?
Here's what I meant about the lips -- I exaggerated to try to make the structure a bit clearer:
'Symbolic' means: there's an inclination people have to draw stuff from the easiest/most symbolic angle, like almond eyes and viewed-from-the-front lips.
Even if you weren't going symbolic and were just copying the lines as you saw them, you weren't thinking of the 3D structure, so missed some details which made it look symbolic and front-on. I put a lot more information in my redline than it's easy to see from the photo alone.
This is why it's useful to either draw from life, or learn structure drawing: photos lack information about the 3D space. It can be really difficult to see subtle overlap and perspective in just a photo.
The stock photo section of deviant art is a very useful resource, a lot is poor but there are some professional photographers who create stock as a service to the community e.g.: http://mjranum-stock.deviantart.com/gallery/
You'll have to register for a free account to see his pics as there are a lot of nudes.
Also, take a look at your colors in the background. I liked the green you had at first because it's about the same saturation level and has the same undertone as Karen Gillan. The bright purpley color in the second version looks very out of place because it doesn't appear anywhere else in the picture. The blue is a bit much also; you don't have blue tones anywhere else, whereas the green you had earlier would go with her tie and walkie talkie.