Bitch overplayed her hand. She just tried to go against the word of a person Koyori was grouping with the whole game and even did a med scan with, while already being sus as fuck.
I also find it kinda funny, that she is telling Koyori that they are not in middle school, while herself playing a middle-school tier drama. The audacity.
At the same time, I find her character pretty sad - she can't trust anyone. She always wants to test people. She tested Hijiri in school and blew up the relationship she cared about, she was testing Koyori's ex with that pregnancy story, she was proposing to test Koyori during the reunion and kept testing her even after that. As someone having major trust issues, I get the feeling of doubt and insecurity, but you have to push past those if you want to have any meaningful relationship in your life.