Ms Understood, I'm just a soul whose intentions are good ... but isn't that a dad joke?
I was thinking that Polythene Pam was also Mean Mister Mustard's sister Pam, because what are the chances of back-to-back different Pams? So that would make her Pam Mustard, presumably, and following that same line of thought, maybe it was Pam who came in through the bathroom window.