I had a hen that was silently suffering(I didn't know) with Water belly, must've been slow progression. She continued laying, but it wasn't until I saw her with a Giant swollen abdomen, a messy butt, & penguin stance, I realized she had it.Then she does not have water belly, aka ascites. If she did she would have stopped laying eggs.
As you mentioned it could just be breeder quality, which is what I think.
When she runs/walks does she waddle like a penguin at all?
I wasn't taking care of the birds for a short period of time due an injury, it wasn't until I started taking care of them I noticed something was off. I was kind of upset my sister didn't inform me of the sick hen.
The hen was so heavy, she had to lay down every 15 seconds. I put her down, immediately, so she wouldn't suffer anymore. It was like her abdomen was a basketball, but heavy with fluid.