This girl keeps stalking me!?

So this girl at my school house has been following me, she thinks i dont see her but i do, and she leaves notes in my desk and everything, she even left one that said "Roses are red, violets are blue, but none of them want your babies as much as I do" but she's really ugly so i don't like her. anyways so the other day I was walking home from school and turned around really fast and the she jumped into a bush to hide. I wanted her to stop following me around so the next day during a field trip to the grand canyon I pushed her off a cliff, except she's following me now as a ghost? How do I preform an exorcisim or whatever?