I have three star chickens, and they are about 18 months old, and all have been good layers. But for the last month or so, one of them is laying an egg that is rough, it does not have the last layer put on the eggshell. It does not seem to bother her, but I am wondering if it is a sign that she may stop laying? OR something is wrong with her laying apparatus? Or is it just an idiosyncrasy of that chicken.