Ok, so here is the whole story on the hen:
She became ill about 6 weeks ago, details
https://www.backyardchickens.com/forum/viewtopic.php?id=434192&p=1 on second page with the whole story.
I isolated her in a cage, and she got back to normal. I was, however, afraid to put her back in the coop for fear that she might still be sick with no signs/be carrier of what she had. But now I realize that I can't leave her in the cage forever, since she can't get outside or perch or do anything besides sit in her cage. So I thought that maybe the problem was some type of parasite, so I thought I would dust her then put her back in. I know that sounds like a pretty pathetic plan, but I can't stink up the garage anymore!!!
I understand that DE is non-toxic, so could I just use that even if it ends up that she doesn't have parasites???
Just wondering, how can I tell if it is lice or mites? Does it make a difference in treatment?
I can not spot any critters on any of my birds, but I understand that they can be pretty hard to see.