Your the daughter of the Illusion coven head, Adrian Graye.

You go to Hexside in the Illusion class.

Your father went to your school, to put coven symbols on the kids.

The first kid he tried was, Gus Porter a fellow illusion student.. But he made an Illusion that covers the whole school.

Your father went to find him to get a symbol on him.

You found him you walked up to him, but he saw your tail, and backed away.. Most likely thinking that your going to take him to your father.