^^everything @Wyorp Rock said, and I would add that sometimes an attack of parasites brings them down enough to reveal an underlying condition that might have been there a while, or lowers their immunity to developing something else. That is, the two things can often go hand in hand and you may...
ok, as I thought. She is an egg laying machine, and has burned herself out. She is only 3 and had stopped laying. This could probably be the end of her life, sorry to say.
Or you could have a disease in the flock and she is the first to succumb. Or she has developed a condition because she is...