Constructive Criticism Wanted

First thing's first; the skin should also be shaded to some extent instead of one, complete solid color. The hair is great on its own, but it doesn't match the rest of the shading. Shading of anything, whether it's a MC skin, a drawing, a painting, etc, will follow the body; this shading makes her appear as if she's very cylindrical! I'd suggest for that to have the darkest spots on the body longer than just one pixel so it can differentiate where her upper body and lower body are within the "body" section of the skin. And then with the eyes, the pupils get brighter where the eye whites get darker; this is more of a matter of preference of if you'd rather the dark part be on top by the hair or on the bottom to make the eyes brighter, but they should be on the same side, if that makes sense?
The shading on the inside of the legs doesn't match up with what's on the outside, and to make the front of the head less flat-looking, I'd suggest raising the bangs up another pixel so you can see more of her eyes, and there's less of that flat darkest color for the hair. It looks a bit odd in comparison to the rest of the hair, which is super highlighted in contrast.

Also, I just wanna say that pony tail is horrifically good?? I never really put them on my skins since I don't do much with female skins, but I've never been able to make them look decent after years, and you've completely nailed it here, wowie
Hope this helps in some way!