I was just talking to my mom, and she thinks that your hen could have been egg bound and the egg may have started to rot inside of her, then she just passed it. When was the last time she laid an egg?
Whoa. I know next to nothing about chickens, and I would be interested to see what the experts have to say. Oddly enough, it kinda looks like and egg roll, like the kind you order from a chinese restaurant. I sure hope you get an answer. Good luck.