This is odd...

[guidofatherof5]

This is a difficult situation as none of us can see or feel the problem. Photos are good but can't replace hands-on observations.
Taking in any food is a good sign and her drinking is important.
I think the next shed is going to answer a lot of questions. I would give her as much hands off time as possible(keeping the stress low) and play the wait and see game. You've got a Vet. involved so some professional advice is available.
My Vet. usually doesn't recommend blood being drawn since garters are so small and it requires a large sample.
Our thoughts and prayers are with you.
Keep us posted.

[Selkielass]

I've seen odd emergency sheds on a couple cat injured garters I've assisted, and they can look really odd, patchy and yes, even fish net like when the keels had seemingly been worn away.

With wild injuries, I've unfortunately found d that a less is more strategy is best. More contact= more stress and slower healing. I only go hands on with very obvious retained sheds, infections and accesses. Anything more than a minute or so of 'help' ends up being so stressful its a hindrance.

Give her as many choices in humidity and temperature gradient as you can. Help her to easily fi d her comfort zone.
Feed wet foods. Gut load.
Rub your fingers with vitamin e oil before you handle her. Don't get her oily, but I have found the oils help scarred and tender tissues to heal, just as they do with mammals.

Continue to watch her behavior and body language. They can't tell us what's wrong, but if we watch carefully we can sometimes see what they need/want more of.

[d_virginiana]

I've only been actually handling her once a day, mainly because I feel like that's the only way I'd notice if she was getting worse, but I try to be pretty quick with that. Other than that, I will move her to her water to soak a couple times a day, as that seems to help the skin (not just immediately, but like for the rest of the day) and she almost always drinks when I do.

For food, it's mainly been whatever she'll take. Mostly fish, which I guess is good since they are so oily?

Steve; you're right. I've tried to take photos of this, but they really don't show much.

The thing that keeps me hopeful is that a lot of her problems right now can be traced back to the trauma of the shed being removed, rather than lasting damage from when it was retained. I may be wrong, but I feel like that has more of a chance to heal than a retained shed would? That, and there have been really big improvements since this started, as well as that odd partial shed when a lot of the remaining flakes came off.
It's been about two months, so she should be shedding again here in another month or so. If there seem to be any complications with that, I'm just going to bring her in to the vet immediately.

[d_virginiana]

Good news update on Harley: When I picked her up today to check on her, I noticed that the 'gloss' is slowly starting to reappear on many of her scales. She's also more 'sturdy' feeling, and less sensitive when being held. She just got the first de-worming treatment on Monday; it's really amazing how quickly this is working after months of almost no improvement.

[Selkielass]

Terrific!!
Fish sounds like an excellent food, especially the oilier safe fish like salmon. There's tons of lore on the net about how good fish oil is for joints, skin and hair.
Chicken liver might be good too, as its rich in vitamins oil, iron and is still easily digested.
My snakes like liver almost as much as fresh backyard worms, buts its a rare treat since oil based vitamins can build up to toxic levels if overdone.