Hen Lost all feathers and is now walking funny! HELP

I have six Australorp hens that I hand raised from babies. They are about a year and a half old. I live on 40 acres and they free range all over and have always been happy healthy egg producing girls. Last week one of my hens dropped about 80% of her feathers in 48 hours. She was acting depressed standing in the corner and didnt have allot of strength. I kept her locked up for a few days on antibiotics and now she seems brighter eats good, drinks and her feathers are growing back in like crazy HOWEVER now she is walking very strangly. Almost like she has had a stroke or brain damage. She acts like she cant focus well and walks kind of sideways and acts like she is going to fall over but she doesnt. She doesnt have a runny nose or irritated looking eyes.

None of my other chickens have any symptoms what so ever. They get dusted twice a year and are in an extremely clean and safe chicken house locked up at night. I have no roosters.

I do live in an area that has black widow spidars and rattle snakes although I dont see a sore or anything on her.

Any help would be great as I am so clueless what could have happened to her and if she is going to pull through this or not.

Thanks Lacy