How do u tell ur ex bff u still want 2 b friends if she thinks u ditched her, doesn't want 2 b friends again??

it was last summer and I heard a rumor that she was goin' 2 ask me to go to the mall with her and then beat me up! (i'm so weak) so i brought my friend sarah to help me! then i though my old bff's friends were behind her so I just kept walkin'. and she flipped sarah off. then she called sarah when she got home and sarah told her that I WAS DITCHING HER!!( which i wasn't) how do i make her believe me and make her be my friend again?? oh yeah she beat up my friends sarah at school too for the whole ordeal. HELP!!