This story feels so very real. The Muggle seaside setting; Marietta's mother with her gentle puppydog pressure; Millicent's world of old Pureblood expectations... and the wonderful way they manage to find each other and make peace, away from the world that has been unkind to them. Your prose is elegant and sparse, suiting perfectly the world of taciturn girls and Wizarding uncertainties you have created here. A powerful piece.