It appears that you ran in to almost exactly the same issue I did a few weeks ago.
Go to my thread I started on Fly-Strike, which is what you chicken got.
I took pictures and posted.
Some of the comments were very helpful.
https://www.backyardchickens.com/t/809129/wound-care-help-please
ps. she is still doing well and loves dog food.
I read that a chicken that has a wound such as this needs more protein and my dog food is 26% protein. Whole meat dog food.
You need quality dog food. Go buy a small bag of Taste of the Wild at your local
Tractor Supply or Orchelins. It has 32% protein, whole meat, not by product. It also has grains and biotin, everything that would be good for your chicken for healing and staying healthy. She also likes bread but it is just a snack. She needs the protein. She wont touch her chicken food.
Also while your at
Tractor supply or Orcheleins, get a $5 bag of Duramycin-10, tetracycline Hydrochloride Soluble Powder. Or just ask one of the worker there to get you Tetracycline. Then with an empty 1/2 gal milk jug, fill 1/2 way up and put 1/4 of this powder in it. Shake it up and poor in her dish. It turns pink after awhile but ok. I found that she likes to have me put the dish next to her and she drinks from it and same with the dog food/bread. She doesn't want to leave her perch. lol
She must not go outside where flies are. The maggots can hatch in just 12 hours. Plus the other chickens will likely peck at her wound and it is dirty outside. Dirt will stick to wound.
I'm not sure why you are still getting maggots. I got a massive amount of maggots out in 2, 20min soaks in Epsom salt(go light on Epsom) not good for later use, just the 1st clean outs. Make sure the wound is submerged the whole 20min in mild/warm water, rub the wound and work out the maggots. Use a very very soft cloth so you dont rub her wound raw.
I'm putting triple antibiotic cream on and Veterycin spray.
You'll find the thread very interesting on all the details.
I hope to be able to take new photos and post them soon.