Reason behind her sarcastic smile

On the very early morning, I saw her in the backyard of our school .She was taking with a cat and watching her gave me some creepy cramps.She was wearing a black shirt with long skirt and her shoes were worn out.I assumed her from my class window down to our backyard where she was. Suddenly she looked up where our eyes met but then she just smiled sarcastically. I don't know who she was and how did she end up at our school backyard. But I wanted to ask her who she was and why was she like that. Many questions was popping in my head but she left the backyard. On my assumption she was kinda pretty and her sarcastic smile was weird but it was like saying that she was okay before anyone would question her.