Thank you for the support, speckledhen, it helps so much not to feel alone. The difficult thing is, this hen seems to finally be out of the woods. To nurse her through this hard time for so long, only to put her down just when she's getting better, feels too cruel to bare. You see, I thought at the start that it was Mareks, but after talking to people on here for quite a while and getting some very helpful input suggesting other causes, I decided against that possibility. The symptoms didn't quite fit, the way I'd heard them described, and I so wanted to believe it was something else. But tonight I signed on here and found a post from one last person, linking me to her thread that described the EXACT symptoms, which had turned out to be Mareks. This is the reason I've dealt with things the way I have . . . now it seems that I've made all the wrong decisions. I could see my way through to putting her down when she was at the worst of it . . . but now, up and around, with so much more life in her . . . I just don't know if I can do it.
What if I were to treat everything exactly as I would if I had her put down, had a necropsy done, and it came back Mareks? Scrubbed everything down, sanitized the heck out of everything, vaccinated every new chick that hatched, used the extra vaccine to inject all the other birds just in case it might help for prevention if they haven't been exposed, even though they are older (what could it hurt?) . . . but just kept her as a pet. I would keep her quarantined from everyone else. It wouldn't be easy. I would have to scrub up between contact with her and other birds, change my clothes, everything. But if I was willing to do it -- could it work?