I just assumed that since I had some new layers in there that it was one of theirs. Yes! I have three 2 yo hens in there. I'm going to get right on those links - thank you!! I'm so glad I posted this instead of assuming!
Hmmmm....So whichever it is - she's two years old. So she ought not to be at the end of her lay. Illness? She doesn't appear so. *sigh* I need to do much more research and much more watching....