She and Maddie were within a year or so of each other at Hogwarts

I would also bet that early in her debutanting Maddie would probably have tagged along with her, especially since she was another trades persons child and they would have known each other from the high street.

I also have Elizabeth Cardew, who is MCHB and who works but is also at the sanditon on a regular basis. Her aunts take lizzy and her sister as companions when they go to the sanditon.