I bought 10 day old maran chicks 3 months ago and all have been fine until yesterday. My favorite one (of course) is strangely off balance and can't even walk up the coop stairs without stumbling backwards. She walks with a strange exaggerated step, falls sideways when laying down, and splays her legs to stay upright. She is eating regularly, but seems aloof socially. (She's kindof hanging behind the others and staying near the coop). No runny nose or sneezing. What could be wrong with her? And should I quarantine her from the rest? My ten pullets are a completely closed flock so there is no chance she could have been infected from another chicken. These are all I have. Thanks in advance!