I have/had 2 California white hens. 5 1/2 years old. I noticed one getting a puffy look to abdomen, she hadn't laid an egg in about a month. she then started hanging back from the group and being lethargic. I decided to check her and felt something not right inside. she wasn't fat, I decided to put her down. she did have internal laying and several yolks stuck together. she also had many cysts all over inside. The second California white, looked very good, same age starting molt, I picked her up and thought hum, she feels heavy, but again she hasn't laid an egg in the last 2 months. abdomen feeling puffy, full, but not watery, acting and eating fine. couldn't feel anything wrong in vent, I went ahead and processed her Saturday, and she is the fattest chicken I have ever done. could not believe all the fat inside her abdomen ,on her back etc. she had NO growths and her liver is just fine. Her ovary had no developing yolks, so she was done with her laying. she went to noodle camp. She is not wasted. I am sad that I had to do it, but I don't regret it. They ate layer crumbles and free ranged most of the day. She must have been a little pig. AS you can see, I made the same call on 2 chickens a couple months apart, different results. You can't always know. I did know the first would not make it much longer due to actions , the second, I had to find out why she was getting so firm/puffy back there before she acted sick. So that is what I did. I don't know if certain breeds are more prone to getting to fat, or just individuals being pigs and coming to the end of their laying life.
Wish you the best and don't feel to bad for too long. Constant Learning comes with the territory.