Oh yes, my goodness...that is a bad looking wound.
I can understand why you are so distressed.
It is Spring, and all a rooster wants to do is mate.
I don't think his spurs are the problem. First, her feathers were rubbed off. Then, the skin was burned by his constant rubbing and wiggle action. Before it could heal,
it got infected from the poop and dirt, under the rooster's feet.
If you've ever had rug burn, imagine someone rubbing it everyday, several times a day. It wouldn't matter how much medicine you took, or put on, or, if you covered it with cloth. The body's attempt to heal the wound, would be defeated every time the wound was vigorously rubbed, over, and over again.
Skin takes a lot of time to rebuild, but first you have to heal the infection. That won't happen if the hen is constantly being mated.
Honestly, I would
keep her separated from the rooster. She is in no condition to breed.
The black part of the wound in very concerning. That scabbing doesn't look right. If she were in my care, I would spray Colloidal Silver on the wound, twice a day. I wouldn't cover the wound, so it can scab over. This would require keeping the hen in a dirt free environment for three days. Perhaps a penned grassy area during the day, and a dog crate for night. After it scabs over, then a hen saddle can go on, (and NO rooster!).
You will have to keep her clean, since she can't dirt bathe right now. Another option would be to use Manuka Honey, medical grade is best. There have been some amazing healings with Manuka Honey. You can also use Vetricyn Spray, I would't use Blue Kote at this point, because I'd want to monitor the color of the skin.
Instead of oral antibiotics, I would give her some echinacea in her water or feed or orally, to boost her immune system. Administer a poultry vitamin, orally, like NutriDrench 3 times a week for two weeks. If you use NutriDrench, 1 mL, is enough. She needs a good nutritional boost.
For two weeks, feed her some extra protein four to five times a week, cooked grains, fresh greens or cooked mixed vegies, diced fruit, and her layer ration.
It's not that the wound is not healing...it's that
it wasn't, allowed to heal.
Anyways, these are my thoughts on your hens wound, I hope they are helpful.
Other members may offer advise, please consider these too.
God's Blessings to you and your hen.