Same as the magic that let Polly get inside at all, and let her listen in on Tom and Mr. Leroy

Right, or that gave the other string quartet the flu ;) or let Polly (and Granny) remember in time.

I think you could write a good "flipped perspective" fanfic pitying Laurel, "queen" of a kingdom that sometimes actively works against her

That's a pretty cool idea! I bet you could even write her as ruthless-but-sympathetic, ensnaring outsiders as she does to try to protect her own family as much as she can.