The only see the Stillwater lab too. Sorry, it was worth a try. Since she hadn't laid in a couple of months, I would bet she was egg bound. If so she might have shown one or more of these: not eating, acting depressed, reluctant to fly or perch, abnormally wide stance, or persistent wagging...
What state are you in? I have "The Chicken Health Handbook" and it has a list of each state's poultry pathology labs. It does give a list of things that causes sudden death: fatty liver, streptococcosis, malaria, botulism, cholera, erysipelas, gout, influenza, listerosis, marek's, newcastle...