Thank you so much for the reply. I don't have any Corid on hand, but I'll see if I can find some locally or order online. My hen seems a bit more energetic this evening and was voluntarily eating greens for about half an hour, and groomed herself a little, so perhaps the Ivermectin is slowly starting to have an effect.
I happen to have some Metronidazole leftover from when my cat was sick a few weeks ago, and the vet thought GIardia might be the cause. I may try giving a small dose to my hen just in case it has any effect, because as you mentioned, she does seem very near death.
Thank you again for the reply!