Have you trimmed the feathers round her vent? Helps so you can see a bit better what might be going on. Also gives the blighters less places to hide. If its maggots you can usually then find if they are on the flesh and flush the wound out etc. Apply whatever is suitable to kill them then.
If worms then again, still worth trimming round the vent.
I occasionally bathe mine HibiScrub (I use it on all my animals, its a surgical handwash but my vet recommends it for skin problems for my dogs and its been brilliant). Of course I understand you might not want to
I don't know of anyone else uses it on poultry. Also I tend to dry my chooks with a hairdryer afterwards. I've only used Hibiscrub on my chooks three times in the past and used cotton wool balls to pat on the affected area with Hibiscrub solution added in the water. Only once dunked a bird in who was a pain to try to just bathe problem area. She smelt lovely afterwards
And was fine. Her bald patches on her back (cock bird treading her too vigourously) much improved. Far less red and angry looking.