Oh my gosh, I am so sorry to hear about your girl! I've never heard of all of these symptoms happening at once! Something must've really gotten to her, so I think that you did the best thing for her by putting her to sleep. Poor dear.
Did you open one of the cyst like nodules to see if you could determine what it was? I would be curious to hear if you did, as that isn't something that I've seen or even heard about before. Ingrown feathers, yes.
I apologize if that sounds unkind or morbid. I don't mean to be. Just scratching my head wondering about what could have been going on.