My 2 year old Barred Rock sex link hen lays big eggs normally and about 1 once a week or once every 2 weeks she lays a huge double yolk egg. Is there a reason for this? She is a big hen and beautiful and healthly. She has never had any health issues and has been a perfect hen. I'm concerned and curious as to why she is doing this. None of my other hens have ever laid one. Any ideas would be appreciated!