So help me...

So I find out Tator's smokin' pot.  In case you forgot, she's 15 years old.  Fiffreakinteen.  I did the usual, yelled screamed and grounded.  I mean what else would I have done?  My question is this:  Once you ground a child, and they screw up again...what the hell else is there?  If I take away all the extras, and she still wants to act like a future convict, what else can I take away from her?  Maybe, it's not about taking things away, but about giving them more.  Like giving her a reason to NOT get high?  But how do you reach someone who seems to care about nothing?  Especially now that I've taken everything away she cares about...namely her freedom.  Any ideas?  Anyone?