Update --
My hen with the prolapsed cloaca is doing very well.
I took her to an avian vet b/c she is a pet. I had not know there was such a person near my until I checked!
First, she had a wound beside the prolapse which was the source of maggots, not worms. I should have researched a little before declaring that she had worms. The maggots were not a long term problem.
Regarding the prolapse, she was cleaned up way better than I could manage myself. 2 stitches were placed in such a way that the cloaca stayed in place for a week, and she could also lay an egg, which she didn't. I gave her antibiotic and anti-inflammatory for a week, then had the stitches removed.
That was 3.5 weeks ago, and all is well thus far.
FYI -- At the first visit the vet gave her less than 50 chance to recover well. At the follow-up, the odds were declared to be in her favor. He initally said that the problem could be one of about 5 things which could only be determined via surgery (which we were not up for). The final guess -- since the vet palpated unusual firmness and tenderness initially that had resolved by the follow up -- was that she had some sort of issue with an egg and that the egg resorbed.
Thanks so much for the advice and support!!!