As a teen, I can say I (and most teens, it seems) have more respect for, and are more likely to listen to, the people that are calm and rational about things. As opposed to those that fly off the handle.
As has been mentioned before, the guilt trip works pretty well. So does making us feel as though we've disapointed someone we respect. Personally, my woodshop teachers oppinion carries a lot of weight with me. I would much rather be punished than feel as I've disapointed him.
I guess you should just remember that your daughter is growing up, and that part of growing up means making mistakes. If she didn't make that mistake now, odds are she would have made it later (since it wasn't a problem in your house, I'm assuming you wouldn't have done any drug-related talks with her). Best she made it now, then, say, when shes just starting her first real job. It would also do to remember that although shes not an adult yet, shes getting close, and treating her like one would be better than treating her like shes 12.
I know I'm speaking from a possition of inexperiance, but for what its worth, you might try talking about this to anybody she really respects, be it a teacher, church group member, sports coach, or any sort of mentor. Have them talk to her about it, and if she respects their opinion of her, she'll probably feel an unplesant mixture of guilt and self-disapointment.
Thats not to say let them handle it on their own, you're her parents after all, but she'll probably respond better to the "you're a smart kid, you know better than to do something stupid like that" approach from a non-family member she has a lot of respect for that to an ***-chewing, and grounding from you and your wife.
