Young Adult Literature
All right: main character, a teenager. She's got family woes, romance woes, and growing-up woes. That makes this a shoo-in for young adult literature. (Not that all adults have that growing-up thing nailed, but we're in literature-land, not the real world.)
Fairy Tale
Because the plot of Ella Enchanted is based on the fairy tale "Cinderella," we also consider the novel to be an extended and fleshed-out fairy tale. And it's a shoo-in here, too. We've got downtrodden protagonists who have magical help in obtaining their goals of ditching nasty family members, getting rich, and getting hitched. Ella effectively does all three, and also removes the curse that plagues her.
Plus with a magic book, glass slippers, a fairy godmother, and wicked stepsisters, how could it be anything but a fairy tale?