It sounds like you could lose her if she continues to refuse food and water. Tube feeding is possible. Could she have eaten something in the yard that has made her sick? Cancer can be common in chickens, but it could be something else. Most state vets can do a necropsy if you lose one, as long...
There could be a reproductive problem, cancer, or other organ issue going on with her. Try offering Poultry NutriDrench 2 ml orally each day for a few days, and mix some mushy wet chicken feed and scrambled bits of egg to offer her. Water is more important than food at first. Are her droppings...