Casey worked up the courage to stay in college because it would raise a lot of questions if she missed class again. If she excused herself from being sick, the four masters would definitely be overreacting again, and Casey didn't want to keep lying to them. She wouldn't tell anyone about Erica nearly killing her. Only Alan knows because he was a witness to the incident. Even though Casey was still a little scared of the girl, her neck was still sore and scarred. She disguised the bruise by applying a few layers of foundation there and adding a red scarf.