This is Melissa^^^^ (I have nothing against Selena Gomez!)
So Melissa and stormy USED to be friends, along with Lynn and Marlene. But just suddenly, she told Marlene and Lynn lies about Stormy making them turn against each other. Poor innocent Stormy had no idea what happened. She soon found out and tried to reason with them but it didn't work. Melissa almost made it her job to verbally breakdown stormy.
She was always jealous of Stormy by her athletic-ness and her looks and her friends. She also tried to get Lily, but Lily knew better. So did shauna, Luke regardless would believe stormy in any situation.
So in conclusion, Melissa is a bitch.
Btw sorry if your name is Melissa! I love PLL and you know how there character is named Melissa and all... Yeh so sooooory.