I think it's great that you have put in the time and love to care for your BIL's chickens, I'm sorry I don't have any advice on the egg bound part, you are doing everything already that I would do for that. Thank you for honoring your late brother in law, it's a beautiful thing you are doing ❤
I have the same question as HeritageFan, are you sure she hasn't stopped laying? They look like a production breed, ie Golden Comet, Cinnamon queen... they lay super well but stop at a younger age in my experience. I had one stop laying at a two years old, now the three year olds are all done...