I have/had 10 sexlinks (they are my pets and have named everyone of them). Is her belly swollen, or is she waddling? I'm no professional by all means and someone else may can shed some light on your problem. I had the same questions as you 6-8 months ago. I now know. I have lost 4 of my girls because they became internal egg layers, sometimes this happens to high production egg layers. They started out loosing weight, their comb started getting droopy and turning gray, being a little lethargic. Then they started to swell in her belly and began to waddle, over some time they became worse and finally passed on. I did a necropsy on the 2nd one because I wanted to know what happened. Her belly was filled with puss like substance and eggs or parts of eggs throughout her frail body, this is how I found out about them being internal egg layers. She had a bad infection as well. My younger hens started pecking them, of course. So I separated them and put them on flock raiser/grower feed (no more laying feed so hopefully they would slow down the egg development). These same hens have laid eggs constantly over the last 3 years, even in the dead of winter. Some of the eggs were extra jumbo size and double yolk. They were just bred that way. I don't know what else to do with them except love them in their last few months. My heart is broke, as of today, my most friendly and sweetest hen passed away. I hope this helps you understand somehow.