If she suffers from diarrhea, or any type of common disease, I recommend you spray some cinnamon powder into your chickens feed.
 
There is a lot of natural cures, cinnamon is one of them.
 
 Is your chicken suffering from a cold shake? Or maybe even a trauma that cause her to lose her appetite? With an effect of not eating, she might suffer from an empty stomach which can be a leading cause to death, since food source for chickens are very, extremely, important health matter.
Identify your chickens stool, is it running? Is there possibly blood in her stool? Act fast as you can, since chickens can have some quick changing dramatic effects and can die without proper care.
 
 
Hope this helps, lifewithpets2016