I once had a goose in with some goslings that I wanted her to adopt, as her previous attempts at goslings didn´t work out well. Well, she wasn´t happy at all, so I let her out for a while, planning to try again later, and she shot off to a nest I´d made up to attract another goose, and promptly plopped one in there! She seemed to be running with her legs crossed!
She laid almost every day, until she had 6, then sat on them, her 2nd brood, and this time they all hatched, as you know. It was so funny to see her, though, so desperate to get to the nest!
So, where´s Missy´s nest, then, in relation to the shed? Can you not fix up some kind of fencing around her nest and keep her close, as maybe her habit of going indoors is what´s interfering? I´d be surprised, I have to say, as if she really wants to brood, she will. but just a thought...funny how geese are, after all.