The poor girl is mentally ill. Everything she does is for attention and not to be "boring". She realizes that the teacher has been paying attention to her (even though only as a teacher) and now she's fixated on him as her entire reason to have a future. Then when the teacher doesn't resist her advances believability is lost. Of course it is only a one shot. If it were a series she could be fixated on him with him warding her off until graduation without becoming a criminal.
Check out the author's other work on this site ( https://mangadex.org/title/61893/a-week-long-relation-between-a-gyaru-and-an-introvert ). It's fantastic.