Good characterization of an unused person in the Potter books, but I think the "sameness" of the writing style makes it hard to clearly identify the character that is telling the story. For a suggestion, try writing the chapter as the person telling the story would write. That means that Hannah's writing style would be different than Susan's. Maybe Hannah doesn't know when to use "me, myself or I". Maybe Hannah is so wrapped up around that all of her comparisons are in relation to her obsession.
I hope that you somehow tie all the chapters into a single story, but if you don't this is an engaging attempt to "grow" little used characters.
If you are taking suggestions, how about doing Lavender? Or even a little known teacher, perhaps Hooch.