I've been working on an edit for a very long time, and I can keep on editing it for a lot more, but I feel I've got down some of the more major than minor points that I need to address here..
First of all, the shape of the girls head resembles more that of an aged woman than a girl. Her cheeks don't stick out as much, and the whole bottom face is much too big/wide/fat. Her face is rounder, too.
Next, the perspective. In the reference, the girls head is tilted somewhat more to the right, affecting the whole lighting of the face. You can fully see the side of her nose, rather than the top of it, for instance.
Your shading and lighting is a bit mixed up, as compared to the reference of course. You're using lighting and shading where you shouldn't, or should use the other. This can be easily seen to the left of the nose, eye, and mouth, where her features add a little bit of shading to the face, which you either forgot to do, or haven't got to yet, which is alright. I believe the mix-ups in your shading and lighting are somewhat caused by the mix-up in the perspective.
I suppose this one would fall in composition. In your latest edit, the girl's eyes look sort of asymmetrical, and slightly looking in different directions. The little bit of the white of the eye we can see under the right eye make it seem as if she's sort-of looking up. She does not look like she is looking at the camera. Also, the shape of her eyes still aren't right either, they are more pointy towards the insides and outsides of each eye. Don't forget to make both eyes look similar.
The errors in and around the eyes are the most important as they are the focal point in your piece.
And a few minor-
The lips in your piece are too round on the top, while as hers go into two, nice, pointy, points. (I can't seem to use a better word today..) And the lips curve inward as they form into those points.
Her eyebrows are thinner.. And I'd like to say they're even, but it DOES look like her right eyebrow either has less hair or is thinner than the left.
Eyelashes.. They add to the piece a lot, and she has them... And you'll notice in my edit I did something similar (And didn't add it to the other eye..
)
I know it's still a heavy WIP, so this probably doesn't apply.. But, you have some VERY similar colors, such as the two dark maroons in the bottom-right corner in her shawl.
It might just be me, but your pallete confused me as well. You might have chosen all the right colors, but used them incorrectly:
5 shades, I circled the areas that I think your shades should resemble.
Sorry, it's very messy. I used dithering in some places, instead of inserting a new color, because I was lazy. And it's my first edit, and I'm generally not a great pixeler.. So, yeah.
Again this edit is far from done or perfect, so take what you want out of it, and don't forget I am very new to art as a whole, and especially pixel art. Really, your reference is all your need to make the best you can, an edit isn't going to show how to fix anything better than the real thing.