Sorry for your loss. A necropsy may tell you what was wrong, but it would be too late at this time. I usually do a home necropsy on my hens that die, to open the abdomen and look for signs of what may have been going on. Sometimes I will see yellow fluid when opening the abdomen, and that is from liver problems secondary to reproductive disorders or fatty liver disease (have only seen one case.) I look at the liver, the spleen, intestines, gizzard, crop, oviduct and any other organ that might have an issue. It is good to take pictures to post here for opinions. Most state vets will do a more thorough necropsy with testing and lab cultures. Below is a vet necropsy where organs are identified, if you ever need to do one at home.

