Without being able to feel the abdomen myself, it's hard to know. Some birds, even the same breed or in the same hatch group, can be more prone to abdominal fat stores (genetics), which can make them feel bloated as well. Since she is laying, it doesn't seem like it's a reproductive issue. Not even sure if kidney issues would not interfere with laying. If you started them on layer at 20 weeks or so, that would be very fast for a problem to develop, not saying it couldn't, but seems less likely at their young age. It's still a good idea to provide an all flock type feed and offer the oystershell separately, there are many things that can affect them laying, so that way they only get what they need no matter what their laying status is. That is all I feed mine, chicks get one bag of starter, and then they are switched to all flock like everyone else.
Make sure you are not overdoing treats, anything other than feed. For those that may be prone to fat, that can really make it worse.