Friend being horrible? Need help!?

Outside school invite her to dinner to say "sorry" for the bad things I've done, and do something bad to her dinner. i.e spit in it without brushing her teeth, put something she is allergic to in it or sommat. You could also tell a teacher that she's being an idiot, or you could save something gross to get mouldy in the fridge and throw it at her in break lol that would be FUNNY DO THAT ONE!!!