So sorry that you lost her. If you would like to find out what was wrong with her, your state vet can perform a necropsy if you keep the body cold and take it is or ship it overnight. Here is a list of state vets including yours:
https://www.metzerfarms.com/poultry-labs.html
I wouldn’t give metronidazole without a diagnosis. You cannot even get that one now for animals, except in a fish powder. Get a stool sample tested. Diarrhea is very common, and depends on what they are eating. Grown hens usually do not get coccidiosis, but it is possible. How is she acting? Is...