Stepsis What Are You Wearing? Thats so Slutty!

First time inviting my younger Stepsister to a frat party and she decides to wear the sluttiest costume I've ever seen! You could see her thong, her boobs, and the worst part is she dressed like this on purpose, she WANTS the attention on her! Well not on my watch… its up to me to make sure none of the boys try to get with her for sex because she's my responsibility. I tried to confront her about the costume but she wont listen… saying that she wants to make a scene at the party and attract boys so she can fuck them!? Then she starts telling me that if I don't satisfy her horny needs, one of my friends is going to… Well I can't let that happen! I'm going to FUCK HER BRAINS OUT so she won't have any crazy thoughts at that party, thats what a good stepbro would do right?