Girls, please help me, this girl is pissing me off! Why does she care?

A few weeks ago this girl got pissed at me one day about my bad grades and she blew me off. Before this happened we would walk to class together and talk a little. Then on the Thursday before last, my friend noticed her tearing petals off of paper hearts and he said she does it like everyday. He asked her why and she said, "Because I want to know if he loves me." Okay well two Friday's ago, I added her on Facebook and we talked from like 9:50-1:30am, and she told me her bedtime is 10:30pm. One of the early messages was this: ME; "I don't get caught in day dreams, just this one moment where my whole life changed. What day dreams are you talking about? The one where your in the forest chasing unicorns?" She wrote: "haha awww thats messed up...why are sneaking into my daydreams o.O ahaha jk its a girls thing nd so i cant tell u wat i think about..." This is just a small portion. And after two Saturday's ago, she hasn't responded to any of my messages. And well last Thursday(last week) at church, I set a row in front of her and their were empty seats next to me. The pastor in the highschool center told everyone to fill the empty seats in front of them and I heard her whisper to her friend about switching sides which meant she wouldn't be sitting next to me. So we got our CST scores this week from over the years and she saw mine and she smiled, it showed all advanced except one proficient. Okay well today in 6th once again she got pissed at me. I was telling my friend that I plan to dropout of highschool next year and he asked her what she thought. She got so mad. She was yelling and she was so passionate. The last thing she said was, "Your not leaving" and I said I am she said, "No your not!" and the bell rung.