beta
i already suspected it but honestly the little brother is right hating his sister. she may not be a bad person but she's a chronic people pleaser and she already probably didn't defend him when their cousin was molesting him as a child (she looks like she knows what happened and still let him stay in their home as an adult) so if that's the kind of stance she's taken about the brother situation he's not wrong for thinking badly of her (imo)
edit: just to clarify, i personally don't hate the teacher character i'm just talking from the brother's perspective