My girlfriend is a twat, what do I do

I've known this girl for a while. She's super sexy and I've wanted her since the day I saw her. The problem is she likes me back and we started dating but it turns out she's a pos lol. She calls people fat, ugly (even makes fun of some of her friends). If someone is overweight she calls them "double chinz". She laughs at people and is super sassy. There's a girl in her friend group that's on the heavier side and she has a troll nickname that she calls her behind her back. The final straw was recent tho.

We are in our senior year of high-school. 18 years old. Theres a kid at her school (I go to a different school) who has a disability. He's in grade 10. She forced him into a corner out of nowhere and started recording with her other friends. She was leading the group. She started shouting "twerk twerk twerk" "twerk man we don't have all day" the poor kid twerked a little and she's laughing her ass off in the video. The kids face was red and looked like he was about to cry. She sent it to me and I'm honestly so disgusted at her actions.

When she comes to see me she always wears jeans and a small crew neck sweater or yoga pants/tights with a small hoodie. Sometimes her underwear will be sticking out when we're sitting down somewhere or she's getting out of the car/truck. The fact she bullied this kid with a disability has me fuming. My question is would I be just as bad as her if I gave her a playful wedgie next time her panties are showing and Snapchat it or get some other girl i know to do it and then dump her stupid ass a few weeks later. Should I break up with her instantly? I feel like this deserves an ass beating( from another girl not me lol) or some sort of embarrassment back. This doesn't feel debatable to me but would u take the high road here or no?