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Terry, what you have there is a chick with Vitamin E encephalopathy, or in layman's terms: sometimes described as crazy chick disease. You may be able to cure her by giving her a few doses of Vitamin E (I nick the end off a gel cap, and get a drop of it into the chick by wiping it on her beak, she will hopefully drink it. Selenium is often given along with the vitamin E. If not treated promptly, there will be other systemic issues. You should see immediate improvement after starting the Vitamin E. Disclaimer: I am in no way licensed to give chick medical information. But I can tell you that this did work for my chicks, though he was very advanced by the time I figured out what was going on, so he did have systemic issues later on. Do a thread search for Vit E Enc. And Cr. Ch. Dz. Reading forward, I see that you've done the research. I'd get a bolus of Vit. E into her along with continuing the ND.
I totally agree w lazygardener . From the description I didn't think it could be crazy chick disease, but after I watched that video it really seems like it, minus the belly up display. I've seen some chickens w the same behavior, same diagnosis. Wishing the best for your chickTerryH