Daughter's First Experiment With Drugs

Mark- I have a 16-year-old daughter whom I have always spoken honestly to about sex, drugs, and the dangers that exist in the outside world. I feel that I have always done as I should to be a responsible parent. Recently, she told me she and her friends tried pot. I explained that this was not acceptable but assured her that we understand that peer pressure can be a horrible thing. We again discussed ways to avoid drugs and reinforced our love and devotion to her, but made it quite clear that this behavior is not in any way acceptable to us. To my surprise she started to cry. I explained that I was thankful she was honest and glad that she felt she could talk to us. I knew she felt bad and told her there was no punishment because I knew she was feeling worse than she has in her life. I also explained that this is her first try and last - that punishment would be swift and stern if she ever thought of doing this again. My question is - what should my next move be, and how can...