Well, that hen is probably over two years old, maybe older than three. The cooked yolk thing could be the last thing you see like that or it could be a sign of bad things to come. It is egg material mixed with solid infection, usually. Look up internal laying and egg peritonitis. That type of production hen is prone to that, unfortunately. I've had way too much experience with it in my hatchery hens, which is why I no longer buy hatchery production breeds. I'm sure you'll spoil her rotten, though. These hens go through so much to produce those eggs!