Chicken moving head side to side unnaturally…HELP!

[AmgkChicken]

One of my hens has been moving her head from side to side not normally and also seems to be off balance. I also noticed she’s the only one that has white poop stuck in feathers by butt. I have covered both coops with Damascus earth and the rest seem ok other than some respiratory hoarseness in their voices. I figured this is because we have had terrible storms with lots of flooding & maybe it was too wet for too long. Not sure about that either. Idk if I need to separate her or if this is parasitic. Mites or lice?

It’s hard to tell in the photo but her mouth is also open and her movements almost look like neurological condition. Bc we live in south Florida and its summer, the rats are everywhere in the coop and run at night and the insects are in full force. I close there feeders at night but it doesn’t help. I’m concerned this illness will spread to the rest of the flock.
I don’t know what to do other than separate her, does anyone have any recommendations? I’ve never medicated the birds other than natural vitamins and don’t have much experience doing so, but I’m welcome to it if it will help.

Please please help

 

[nuthatched]

What's Damascus earth? Diotomaeceous Earth? I'd go scrape it out, it's a respiratory irritant for you and especially your birds.
What's your birds diet?
To fix vitamin deficiency, give 400i.u vitamin E capsule and about a third of a B complex tablet every day for a few weeks. Any brand from the grocery store.

 

[AmgkChicken]

Thanks yes I mean “Diatomaceous earth”, their diet is comprised of Dumor organic layer crumble, worms, Cluck & Co.layer blend(oats, peas, corn, barley) oyster shells & fresh produce. They also get probiotics in their water every other week & vitamin B complex. I don’t think it’s a diet thing as far as what they are eating bc she’s the only one suffering and seems to be having a hard time with balance & leaning back on her hocks occasionally. I will try vitamin E, hopefully she eats it. My concern was also mareks but haven’t had any experience with it.