I get that it was not maliciously. She didn't notice that it was his notebook at first. I understand. I don't blame her for that. I don't even blame her for wanting to give it back naturally. Whatever.
But she HEARD his reason for talking to Tomori. She KNEW he was being completely reasonable in his conversation and Tomori was the one overreacting. Despite all of that, she starts an argument and BLAMES him for being bad to Tomori.
It is one thing to be a socially awkward ball of anxiety when situations happen that are not your fault. She CAUSED this. You are ignoring that.