I am looking at this as a former user and not a mother (I am 29 years old and my DD is only a year, so I simply wouldn’t know how to talk to you as a mother in this area). And I apologize in advanced for the long post.
First of all, as some other posters said, pot has a reputation for being harmless and not being a big deal, just look at how it is often portrayed in the media. For the most part, I don’t think that it is. I think the worse thing about it is that it is illegal, and therefore getting arrested with it could seriously change one’s future.
Secondly, she can be honest when she says it is just a social thing. I know many people who smoke that are similar to drinkers, they only smoke at parties where others are smoking and they may never buy it themselves. Honestly, in my college days I saw way many more drinkers going to the ER than pot smokers (come to think of it, I don’t know any that ended up in the ER) and again, many more drinkers got kicked out of school due to poor grades or discipline problems (because they were too hung over to go to class or did something stupid while they were drunk, like setting fires to things, etc) because they drink too much.
I don’t want it to come off like I think that it is ok to smoke, because I don’t. I certainly could’ve had better grades if I didn’t, but I don’t think that you should panic, which brings me to my third point. Don’t panic and freak out on her. My mother did that in high school and all that taught me was to never tell her anything! If you remain calm and tell her that it upsets you and you don’t want her to do it anymore and there will be consequences if you find out that she does (especially if she promised she wouldn’t and this is something that you can do, probably easier to do if she is still living with you or you help her financially), she will respect you a lot more and therefore try harder to please you.
Fourthly, make sure it is just social and not something else. I started doing drugs because I was severally depressed due to past abuse issues and an un-dx bipolar disorder. This is why it would be good to get her to see some kind of T or counselor, but just don’t push her. If she isn’t ready to go to one, nothing will come of it, except resentment of you.
Lastly (I think

) I know some people have posted that you should tell people because these types of things thrive in secrecy. But, honestly, it depends on the person. I didn’t care if anyone knew I was smoking. My parents could have told my whole family, church, school, whatever. I really could have cared less. To some people, though, I agree, they may become embarrassed, so I guess it depends on what type of person your daughter is.
Overall, it sounds like you are taking the right steps. Just remember, many people use drugs (especially pot) at some point in their lives (most often high school and/or college) and grow out of it after a couple years. It is actually amazing how many people do do drugs, and you really don’t realize it until you start doing them and hanging out with those people. I saw college professors, doctors, lawyers and the usually artist type people and students. Some people will smoke all their lives, but for most, it is just a fad.
For me, knowing that I was leaving college and that if I got arrested, I probably wouldn’t be able to get a job was the biggest factor in getting to stop. Staying away from friends who would pressure me to smoke, after I stop, was also a big one.
I hoped I helped in some way. I hope I didn’t offend anyone either. If you want to ask me anymore questions, I would be happy to share more, either here or by pm.
KB