Is it a young bird? It make just be getting into the swing of laying. If it's an older hen, is it molting? Molting sometimes brings on rubber eggs. Either way, I'd offer more calcium and (if you're treating), less treats.
she has been laying for about a year now. I'm not sure is she is moulting, as she is completely bole in some arias (don't know why) for a couple of months now. we have tried a saddle for her, but it didn't seem to work.