Threatened

Can someone tell me why girls have to bring each other down? This girl shes hated me since day ONE and i dont want anything to do with her. Yes i have a past that will always be my past but im trying to move on from it. Im happy being me! Im happy trying to be the best me. No drama. But why does she appear out of no where?! why does she have to hold me down?! I feel like im trying my hardest to be the best me i can be but there’s someone holding on to my foot making it so much harder to be happy. How do i get rid of her hold? How do i be happy knowing she will always pop up..?