[TheClassicCarKid]

yikes...I know older people don't agree, but you have to realize that at this point in your step-daughters life, what other people at school think of her is probably the most important thing to her. And right now she's the girl with the crazy stepdad. We knew a girl with a dad who did that, and that was the last party anyone asked her to go to. You may not care if that happens to her, maybe even think it's a good thing, but that is HORRIBLE for her. No reason to get the police involved, hold your stepdaughter responsible for her actions and end it at that.
On a related note...
When I was in school my parents told me not to drink, but if I did they told me straight up that if I was drunk or my friends trying to drive were drunk that they'd come and pick us up and take us home. I feel like that's a really important conversation to have and might save some lives.