Alternative Character Interpretation: Gwen's father. The books portray him as the Only Sane Man in a household full of brainless women, trying to turn Gwen into a decent woman despite the mother and governess ruining his efforts. But he apparently hired Miss Winter (a complete airhead) and saw her and his wife spoiling Gwen rotten for years. He didn't check if Miss Winter was giving the child a proper education (she wasn't). And when Gwen turned to be an absolute Spoiled Brat his solution was... send her to a boarding school, far away from home, and let the teachers clean up the mess.
Designated Hero: The 'responsible' form teachers. They are nasty to every girl who doesn't fit in their picture of the perfect Mallory Tower girl yet supposedly have the right to do so and are portrayed as Reasonable Authority Figures and obviously favor students like Darrell and Sally.
Maureen in the fifth book right after her arrival. You're supposed to dislike her because she talks and (to be fair) brags a lot but she just seems to be really excited (and probably a little nervous) about her new school which is why she's overly talkative. Considering that she just wants to make friends and/or new contacts one can feel sorry for her because the others instantly dislike her because new students are supposed to be quiet.
Catherine from the same book. Sure, she's an over-the-top goody two shoes wannabe, but she was genuinely trying to be kind and helpful only to get constantly blown off and mocked by the other girls, and you can feel quite sorry for her when Belinda humiliates her with a caricature in front of the whole class, everybody laughs at her and she leaves the room crying. Yet she supposedly deserves it and Belinda wasn't being mean, but funny and responsibly teaching her a lesson.
Gwen to some extent. She is lazy in class but she is behind in her education because of Miss Winter's bad instruction, yet the teachers have zero patience with her from day one. In a later book, when she realizes why the girls hate her, she tries to be more sensible, and the other girls ignore her self-improvement because she's "never done anything to make herself likable" and she left it too late. The fact that the girls know she's trying to work on herself and just ignore it isn't really fair, especially as it takes away everything that makes her unique.
What an Idiot!: Gwen. She tried to skip the exams by faking a heart condition and didn't think that she would be, you know, examined by a doctor.