You can't tell what made a chicken die by looking at the outside of the chicken. It requires cutting the dead chicken open and examining the organs and other abnormal things you might find in the abdominal cavity. It's called a necropsy.
You can do it yourself and take photos of the organs and anything else you run across inside her , and we can help you figure out what you've found. You would be surprised at what we discover inside a chicken - body heat cooked eggs, soupy fluid with tumors floating in it, liver enlarged to twenty times its normal size, spots and tumors festooning organs, etc.
Or you can find an animal testing lab near you and have them do a proper necropsy with pathology testing to see if a disease killed her. If you wish to go this route or do the necropsy yourself, refrigerate the body until you decide what to do.
Too bad you haven't indicated your location. We could help you find a lab.