My hen did this so same thing. Merecks is what everyone told me I didn't want to believe it ,so I did some Google searching. Then I immediately isolated her
(MaryJane) brought her inside keep her warm with heating pad I gave her vitamin water she liked the dragoon fruit, i have her 12cc every 3 hours or if she wanted more I gave her more. I feed her meal worms live ones (protien) Everyday she got a lil better but couldn't walk and then one morning I thought she had died she was so weak couldn't hold her head up lost anda tone of feathers so thin and would act like she was crazy. after everyone telling me and all the reading on merecks I thought we were going to have to put her down. At the feed store this wonderful elder man asked me if I needed help as I'm reading all the medicines and food some to save my MaryJane.I told him everything that was going on. He smiled and handed me a bag of diatomaceous Earth.. Ok I only had seen this fine white powder once before ,my dad back washing the pool. He laughed and said yes but this is Human grade. He told me to dust the hell out of the entire flock clean our the coop dust everything and the birds two three times then regular routine and she will come around honey don't give up your birds have mites.. the first thing of course was.... I started to itch then he chuckled said you can't get um just the birds. Well I did and I happy Mary Jane is walking she has new eathers like a new girl. she is still a lil wobbly when she wakes in the morning, her nickname is twinkle toes but she better everyday. Don't give up and dust the hell out of everything