
I found the colors to be uninteresting and so I swapped them for more dynamic colors – whether you feel the same tends to mostly be a matter of preference, ultimately I've gone in rather quickly and in a sketchy way to try and get across the advice I think you're looking for, and I think the more varied colors push the piece in a better direction.
I'll give some notes on why I changed what I did. Keep in mind that most of art is intuition, there are no rules, only what works. Even what I've done I can clearly see areas where it lacks and could be improved – or maybe areas where I am wrong. Take what helps you from my advice and ignore the rest.
-Stray hairs generally follow the trend of the rest of the hair, only displaced, so I've brought them more in line.
-I've darkened the background to a more neutral tone in order to better show off the piece. In most cases a 50% light/dark background will best show off your pixel art and is a good general choice.
-I've added highlights to give a better sense of form and contrast.
-I've separated the hair into smaller, flowing, often overlapping chunks. I think this is the most important piece of advice you could take away from my edit: hair is messy, somewhat random, but adhering to a gravity based pattern. Locks of hair are falling, getting tangled, overlapping, twining, etc. Even with straightened hair you will see areas of overlap and twist.
-I've added interest to the silhouette of the hair by pulling it in places, flattening it, indenting it, basically not allowing it to be a perfectly smooth shape. Specifically I've pulled it in over the right shoulder, flattened it on the left side of the head, and indented at the part of the hair.

(Example of the silhouette difference)
-For the skin, I've darkened the areas where skin meets hair, and kept skin light where it overlaps hair. Also when hair overhangs the skin like with the bangs the shadow tends to be displaced, so you also benefit from not darkening the skin there, though in this case I was doing a quick pass and did not add in the drop shadow.
-I've somewhat disrupted the line of the left shoulder with the hair overlapping to give a more dynamic feeling overall. When I say dynamic feeling, I mean it feels like the hair has a 3D position, rather than being a 2D sticker located on or behind the body. On this topic I would say that you're probably further along than you think with understanding hair as most of your pieces have a very good 3D sense if lacking somewhat in other areas mentioned.
Now I am speaking to Chonky Pixel. I understand that you've not opened this thread wanting to be critiqued, but by giving critique you are opening yourself to the conversation.
I find your advice quite troubling, in that it showcases a general lack of understanding. In both cases of your modification, you've cheapened the overall shape by failing to see it and instead faulting the 2D shapes which create it. The L is not just an L, it is part of a community of shapes. What you may be seeing as problematic with the L or T shape is a problem of integration not something as banal as shape choice. To prove this, I've not only kept the L in my edit, but added a few more.
To quote you:
I agree that the hair is generally on the right track. Some clusters need tightening up though, more work needs to go into the shading, the line work needs cleaning up, and for some of the styles it needs some texture added.
I honestly find this insulting, and while I can't claim to know your thoughts behind writing it, it comes off more as aggression than critique, a laundry list of vague and useless points without actual solutions that appear meant only to put down the original artist, who frankly has a better grasp of 3D objects than you do. Critique is meant for learning, both for the critic and the critiqued, not for the chance to insult someone who has made themselves vulnerable by putting their work on the line. Please open your mind to the idea that the person you are critiquing may understand certain subjects better than you do.
To go in further, the idea that something needs to look good close up and good far away is absolute nonsense, and I don't know where you got the idea from. I'll give you an example. This is a boss portrait from Final Fantasy Tactics, zoomed in.
https://gyazo.com/4b362dad4717d0912b6e3b4fd1c20671And this is the full piece.
https://gyazo.com/77db029e3faa411a6a92480d23e49439You can see that it is not a matter of individual shapes or pixels, but a matter of cohesion. Zoomed in all the way it looks like soup. Zoom out, at the resolution it was meant to be seen, and you start to see the communication between shape and color that can be missed so close.
While I found your critique insulting to the original author, I want to be clear that I'm not attacking you as a person but your critique, and I do hope you continue to critique, just in a more open and honest way, rather than giving with utter confidence rules for how a person should go about their creativity, and insults thinly veiled as critique.
I'll leave for tecnologgamer some other examples of pixel artists drawing hair in different styles that I think might be helpful.

(A portrait by me, also an example of a bright background working to highlight the piece)

(Various portraits from Final Fantasy Tactics)

(Various portraits from Disgaea)

(Various portraits from Advance Wars: Dual Strike)

(An example of an entirely different way to do hair – unfortunately I don't know the artist)