I have a hen that walks backwards from time to time.
She’s had this problem since birth. Her mothers eggs got disturbed in the last three days of incubation and I believe this hen suffered some neurological damage at birth.
She’s 18 months old.
She is moulting this winter and regrowing feathers that got ripped out
Recently her backwards walking has got more common, often in low light conditions.
Her condition may be worse due to her molting, I would try the Vitamins to see if those make a difference.
For the medications - discuss those with and use them under the guidance of your vet.