stupid girl at school! i need help!!! and really faaast!!!!!

ok i missed one jour of school and that is when every student in my class is being interviewed par the police because someone tried to burn down the school because they thing muslim kids are being trained to bomb places. anyway that isnt the main problem this chienne at school started saying things behind my back like "that stupid secretary" (i beat her at the elections) and alot of other mean stuff i dont remember but my bff told me about it and i am crying so much, i feel so angry and hurt. what should i do when i go baCK to school tomorrow and i only have a couple of hours until i have to go to lit so someone PLZZZ help me i REALLY need advice!!!!!!