Help ME Please (1)

ok, there is this kid at school. She used to be my friend. Lets begin with the story. So, i told someone who she liked and that C*nt i told is another story. That C*nt told my ex-bestfriend that i told EVERYONE who she liked. She started ignoring me.So someone randomly told someone her phone number and she blamed it on me. She wrote me a stupid message on my instagram account right? so i posted what she said so she would get my reply! My friends were sticking up for me and she told them to piss off! The next day, that weak girl told my friends which split the WHOLE group up and she also told the f***ing teacher! following on the whole class and kinda the school knows what i did but they dont know what she did! now most of the school day i have to be alone and that ex-friend always stares at me, like i was videoing her to see how many time she looks at me and it was like 5 times in 58 seconds... Please help me, i dont know what to do