How to feel happy when she just ruins my happiness?

Are you serious? Your so called friends are intimidates by the girl, they see her pick on you and don't want to be picked on so they try to stay on her good side. You sound very young, so either talk to your friends about how crazy this girl is, how much it hurts you and if they don't care, slowly stop being friends with them. I wish you the beat sweetheart take Care