She's 2.5 years old.  She has been treated for fleas, and none of the other animals have fleas.  We sweep, vacuum, and change appropriate bedding on regular intervals.

Problem:. While we were battling this last round of fleas, she chewed her skin free of the hair in several places, especially around her butt.  Kinds looked like a baboon for a while.

We got rid of the rash and her inflamed skin, but now she has a dry and peeling thick elephant looking slough.  No visible fleas, but she Is constantly - and I mean constantly digging into her dry areas.  She must be itching like a Mofo.  I can't get her to stop.

I've used several anti itch products, several medicated creams, all kinds of baths, flea pills from the vet, Benadryl....

I don't know what else to do.

She is gonna start drawing blood soon.  And that constant chew chew chew sound is getting me to want to start drinking again.

Help me ARFCOM, your my only hope...

I've got a 7 year old GSD that presented with skin problems at about 2 years of age. I have spent thousands of dollars on vet bills. He would get these stinky yeast infections from dermatitis and the vets couldn't pinpoint a cause. I finally took him to the Uof I Veterinary college and over the course of two years they tried to find the source of his skin issues. From Special prescription Kangaroo meat dog food at $200 month to weekly injections they tried everything. The injections were working well but during Covid they became unavailable. They only thing that works now is to watch him closely and as soon as a sore developed treat it with this over the counter mousse the college recommended. Treat the sore and then rub into the surrounding fur to knock it back before a yeast infection takes hold.

https://www.allivet.com/product/douxo-chlorhexidine-climbazole-mousse-for-dogs-and-cats-6.8-oz/50260.html

If you've had fleas before (especially recently) and are not on any monthly flea/tick preventatives there's a good chance you are dealing with fleas even though you don't see them.

As i typically say, i would recommend a vet visit and further workup. Given your location and your dogs age there is the possibility it could be allergies (environmental vs food).  I'd start at the vet.

Have you tried changing her diet?  My 7 yo female GSD has had itching issues.  Over the years we've tried Apoquel and Cytopoint.  Both worked, but both are expensive options.  My vet prescribed Prednisone, it's inexpensive and it worked.  I was concerned about the long term effects so we tried another cytopoint injection and in the meantime I eliminated everything with chicken from her diet.  It's been 3 months and she stopped itching, until this week but she's going into heat and blowing coat.  I feel really terrible that it took so long for me to realize she was allergic to chicken.  It was difficult because we use chicken in so many of her food sources.  Her favorite treats were Nubs from Costco, "made with real chicken" and my dogs have consumed Costco rotisserie chickens more than we have.  No more.  We've switched to turkey and she hasn't shown any reaction.  It takes at least a month of not eating the culprit to get out of their system, maybe as long as 3 months.  We haven't had fleas but we still vacuum everyday and steam clean monthly.  My garage is filling up with used vacuums, there are at least a dozen out there and that doesn't include the 4 we have in the house, 2 up and 2 down.  So I feel your pain or at least have felt it, it's tough on your pet and you.  The other thing I'd suggest is bathing her frequently but make sure not to dry her skin out too much either.  I've accumulated a dozen or so different types of shampoos in my search for relief.  Even have used Listerine, apple cider vinegar, and Selsen Blue as well as oatmeal and green tea shampoos.  But the only thing I figured that worked for sure was eliminating the chicken from her diet. Good luck.

No fleas (year round prevention).
Dogs kept indoors.
Bullmastiff has zero skin issues.
GSD has skin issues.
Stopped feeding GSD dog food with chicken.
Bison and lamb was worse than chicken.
Now feeding Pro Plan and Blue Buffalo sensitive skin both with salmon.
Have tried Apoquel and Benadryl (cheaper and OTC) a steroid cream Murcin (prescription) seems to help as does Vetsan which is OTC.
Best I can do so far, temporary elimination, skin problem comes back, try to keep it in check.
Bathing seems to make skin issue worse, not better.
Vet says FL is bad for dog allergies but he had the same issue when we lived in KY.

Glad I'm not the only one.  
One of my boys (GSD) has the same problem.  He's given himself some pretty good hot spots and has had to wear the cone-of-shame a few times.  
I've tried different diets and supplements.  Currently he gets a daily Apoquel pill.  It seems to work.  
Sometimes he starts to chew on his tail.  I double his dose (one in the morning and evening) for a few days and that gets him through it.  
Stuff is expensive but he's worth it.

It's a pain in the arse trying to figure out how to make our pets feel good when there's something wrong and they can't speak.  I've had two Shepherds where one itches and the other doesn't.  Making it more difficult, the one that itched was always in the house while our male roamed outside a lot. I guess there's no easy answer.  I've had good luck with Bison, Lamb, and Venison by Merrick.  Bathing can worsen the problem because depending what's used the skin will become more dry, I've spent hundreds on different products to wash them.  All trial and error.  One thing I forgot to add was I supplement their diet with fish oil and vitamin E, supposedly good for skin issues.  The last thing I'd recommend is expensive, that's why we stopped, is going RAW.  When my dogs were on RAW their coats and health seemed amazing, but when my wife noticed I was spending more on their food than on own it didn't go well for me.  Some months I was spending double for them.  But damn if our dogs didn't seem to really thrive.  I'm doing more of a hybrid diet now, a little RAW with traditional dog food.  Once our contract expires with our breeder we're going to switch to making our own food for our dogs.

My oldest GSD had these very same issues. Seresto collar is a must. My step mom would brew up tea and set the teabags on her hot spots. I think she used something else too, but the shit worked. Idk how.

See a different vet, see if there's fungus or anything else involved.  If not, you may have to just put her in a cone.

My last dog had that thick scabby stuff, vet checked several times and said it was just allergies. We tried changing diet and all that, nothing helped. Finally, I pulled one of those scabs off and looked at it under a microscope I had and saw the little mites myself, it was mange. Had to bathe him many times with special shampoo and all that to get the bastards.