Thank you all for your help! I really appreciate it.
@Ursuline Chick Unfortunately our chicken vet is out of town until February, but we do have his email. It sounds like iron would be good for her, but I don't know where to start with that for chickens. We have been feeding her baby food with a syringe (a tiny bit at a time in the tip of her beak, careful not to get any down her throat or tilt her head). She's not acting herself, normally she's the boss and she's just sort of hiding now. She is interested in drinking, so we've gotten her to drink a little unflavored Pedialyte.
@Aunt Angus and
@Eggcessive I'm not familiar with MG, but I'm reading about it and that does seem to match her symptoms...I'm hoping that is it, since it sounds like it's treatable? I saw they sell the Tylosin at TSC, so maybe I'll pick some up.
She's not currently isolated, but the other 3 chickens do seem fine. I checked them and no swelling, eye issues, or lesions in their mouths. They're all eating and drinking fine, acting normal. My mom said Kitty started getting sick several weeks ago (I live out-of-state, but home for the holidays), so I would think the others would have gotten it by now if she was contagious? I don't know, though, I'm not familiar with these diseases.
For the ivermectin, is it better to use the pour-on? I thought I'd have to give her something internal since they're on her face and in her nose, and I can't really pour it on her face. I've never used it, though, so I don't know which is better. Egg withdrawal isn't an issue, she's post-henopause haha. I did spray the coop and roosts down with Permethrin about two days ago.
I'm wondering if the mites have taken over because she's weak from being sick? Or maybe she's just old and frail? She's going on 10. The others have very few or no mites at all, and they don't look thin or sickly.