Replying to Psycho bitch ass ex girlfirend

my gf told me that she just wanted to be friend a week before prom because she wanted to be single and figure her life out on her own. i was like thanks bitch right before prom no less. anyway she takes a seperate car to afterprom because she has to work in the morning. she left afterprom at about 1am because she had a migrane and needed to rest for work. the next day i found out that she ditched me to go fuck some dooshbag whos a piece of shit from head to toe. anyway, i confronted her about it and she denied the whole thing and said that she really did want to just be single for awhile. so i told her to go fuck herself because i have proof (she told one of my good friends her whole plan that night). the next day she tells me that i scratched her car when i sat on it a few days ago. except i was wearing a tshirt and jeans with no rivets or anything abrasive on the back of them. so basically shes a psycho whore and i wonder what i should do with her.