Just film them with your phone and tell them you've already sent it to the school authorities... or better yet, to someone who WILL send it to the school authorities, unless they stop bullying ANYONE and act as your servant bitch for the rest of the school year
wait do they have cameraphones?
Nope, I said that bc of the OP's title "If I was Camilla"...
STILL, in other stories with similar setting, they DO have some stuff like that... Like for example magical devices capable of recording audio (as in "I Am Trying to Divorce My Villainous Husband, but We Have a Child") or even stones capable of recording audiovisual footage ("My first kiss with the evil butler", "No, I only charmed the princess!")
I would definitely grab the scissors from that bitxh's hands and cut HER hair without any hesitation at all.