Personally, I would stop by the police station. I'd probably take dear daughter with, so she can hear it firsthand that she doesn't get to make these choices yet.
A couple questions - are you sure it's a 22-year-old, as opposed to a younger kid (not that it really makes any difference I guess)? Where was she having this conversation and can you shut it down? Is she already on 24/7 supervision?
So sorry! These kids can sure keep us on our toes.