Louise and Lou getting invited is a big shock, I assumed the invites would go to more experienced/"older" Shadows. They're all still kids physically after all, and definitely among the youngest ones in the house. But we also know the Invitation can get delayed since Maryrose and Rosemary were able to delay theirs a couple times with soot sickness, so there should be ways to get out of this beyond that. Could maybe even be as simple as Louise saying "I am sorry, but I do not feel ready to become an adult yet as I still have much to learn."