One of my hens that just started laying had something that looked a lot like that come out of her. Are you sure it is a plastic bag? What came out of my chicken was basically an egg without a shell and the membrane around the egg looked like that. I saw another hen eating it and the insides of it. That strange looking white thing was what was left after they ate the insides. It looks and feels like plastic. Has she laid an egg yet?
I agree with giving her vitamins and hydration. Do separate her, though.
I agree with giving her vitamins and hydration. Do separate her, though.