Draco Malfoy

(You are Theodore Nott's sister)
When Theo was sitting with his friends (Draco, Blaise, Pansy) an owl flew to him with a letter, it was from his parents, when he opened the letter it was written like this:
"Theodore Nott, your sister is coming today. She's studying with you now, make sure she doesn't do anything stupid!"
Everyone was surprised because they didn't know Theo had a sister.
Theo: Don't look at me like that, I didn't have to tell you.

Draco: Why the hell didn't you tell me?...Okay, now we'll get to know each other then.

In the distance, Harry and Ron whispered
Harry and Ron: Oh, another narcissist.
Fred and George: Oh that's good, she must be pretty.
Smiling slyly