X2 on everything said here, I lost my precious hen Daisy last year to egg yolk peritonitis...she had had problems with internal laying before, recovered, and then struggled again....and the second time, we had her put to sleep, we knew it was time, her abdomen was swollen with the infection, and...
Runny nose or cough? Can she stand? When did she last eat or drink? What does her poo look like? How old? Is she laying? Certainly keep her isolated....getting her to drink I would say is item one...