Do you want to find out what was wrong with her when you lose her? Most state vet labs with perform a necropsy and can diagnose what was wrong. The body must be kept cold, not frozen and taken in or shipped overnight. Many people also do home necropsies, and it can be a good learning experience...
Hens can suffer from several things, like reproductive issues (salpingitis, EYP, soft egg shells, cancer,) crop problems, worms or other problems. Those can lead to diarrhea or soiled vents. Does she normally lay eggs anymore, and have her shells been normal? Is there any swelling or enlargement...