So sorry for your loss. If possible can you refrigerate the body, and send it in to your state vet vet this morning? That could get a diagnosis, and help to ease your mind. Tell the state vet that you are a backyard owner, and need to get a necropsy. There are several (six) poultry labs in NC...
You might need a flashlight and another person to hold her while you look inside the beak. Yellow plaques or caseous deposits sometimes can be found in the beak when they have canker (trich,) wet fowl pox, or thrush (fungus.) Sometimes a respiratory infection can cause deposits down inside the...
First before I started with drugs, I would try to determine what is causing her to hold her beak open. Do you still see mucus inside her beak? Look inside for any mucus or foreign body, or yellow gunk. Do you see any watery or foamy eye or nasal drainage?
Feel her crop gently, and note if it...