Sorry for your loss. Most state vets will perform a necropsy on a bird you lose if you keep the body cold in the fridge, wrapped in plastic bags. They can diagnose things like canker and other diseases to know what you are dealing with. That is something to keep in mind if you should lose another bird. This is a list of state vets:
https://www.metzerfarms.com/poultry-labs.html
https://www.metzerfarms.com/poultry-labs.html