I would try the vitamin E and B complex that Wyorp Rock recommended. It is possible that she is suffering from wry neck and imbalance, but Mareks disease could also be possible. Other possible things that cause neurological symptoms are head injuries, vitamin E deficiency, toxins, and heavy...
I don’t see the video yet. Those are best uploaded to YouTube with a link posted here. How old is the chicken, does it lay eggs, and could it have suffered an injury by mating or jumping? Is she doing any better now? Can you get her drinking some water either with a tsp of sugar per 8 ounce cup...