Thank you both for the excellent critiques!
Here's my current version, with the very important caveat that I haven't sorted out the jaggies or done anything with the hair yet (the nature of which is a bit different with the new background colour):

1) Hair. But I definitely see the decision to use less detail. I still wonder what a bit of detail would do.
2) That bright highlight above her right eye stands out. It's easy for me to say simplify it, but maybe you've already tried that and you settled on what you did.
I haven't ignored either of these points. For half of its life, the image actually had some scrawled details in the hair and it didn't feel quite right, but I never refined them. With the new background, I think adding detail into the hair might be overkill but I'm still considering it. What I will definitely do next is work more on the edges of the hair, which I didn't think was as important before. My original intention was to capture the frizzy curls with small sweeps done on my tablet and I barely refined them after that, but now they definitely need work to fit in with the lighter green. After that, I now feel like some subtle detailing around the outer edges of the hair might work very well.
As for the brow highlight, I have an idea why it may not be working. It's one of the areas where the shading goes against the scan line philosophy and the lines are vertical instead. That may be causing issues, or is the entire presence of that section of highlight problematic?
I've dramatically simplified the watch, having definitely chosen the artistic license route. It's still a bit rough but I think I've cracked the general way I need to go about it. I've tried to emphasize the screen and the octagonal shape to help it shout 'watch!' instead of 'bracelet!'
4) I go back and forth on the dark shadow at her neck. I love the highlight and mid-tone colors meeting each other, but then the dark tone is just a line with no dither.
That completely flew under my radar and I've hopefully addressed it. Thanks as well for the very kind comments.
1: Lips. You want to learn how to imply forms, but you're using a lot of outlining around the lips. When outlining isn't explicitly part of the style, it can look unprofessional to me when it's used to separate areas like this. I would try removing a few outline pixels and adding a few just at the edges of where your two difficult shades meet.
Thanks so much for the helpful edit. I agree about outlining and it's something I'd like to avoid with the style I'd like to develop. I'm worried I may have gone a little overboard in removing the outlines, but I do think it's improved the resemblance and still reads as a mouth. I suspect it's possible to get rid of more of the dark pixels on the left side of the mouth (for ease, I'm describing the sides of the image rather than the face) but my current attempts have suggested that they're all load-bearing as it currently stands. The new mouth also made me realize that the philtrum area was too long, so I've moved the face down above the mouth.
2: The way the original image is composed, you have the light skin, framed by dark hair and uniform, which itself is framed by light background. Honestly, I don't know if this follows any well-known conventions of composition or anything, but it does serve to make each element really easy to read and understand. By choosing a dark background, you've made the hair and uniform almost disappear. This seems like a shame to me, as you've got some great detail work in the uniform and the hair could be so much more! I'm sure you have your reasons though.
I think my reasons were subconscious and bad, and I should've tested out every colour in my arsenal as a backdrop just in case. Suggesting the lighter backdrop has really changed the whole piece and I agree that the jumpsuit and hair look much better now (although, as I mentioned earlier, I am now going to work extensively on the hair to make it fit with the new colour).
Regarding the jaggies, I am going to hunt them down but I wanted to post an update first in case I've broken anything in my new version. If the piece you wrote isn't too hard to find then I'd be very interested in reading it.
Thanks again!