I really like your Millicent and Dudley - not perfect, but fully fleshed-out (um, unintended pun) characters. I'm not sure Harry as I see him could be quite so unpleasant, but since this is from Millicent's point of view...
Anyway, this is a lovely story, and the ending is fabulous! I love the whole idea of the book, and the cover, and Millicent being so forthright.