I'm going to repeat what others said and add my own thing for what it's worth.
I, first of all, want to thank you for being direct with your girls, no matter their age. It seems that very few CF parents do that these days, because things like (hey, if you want to live, I suggest you do your meds) are NEGATIVE BOOOOO!!! Haha. I think it's the best way to go, though.
I think what Ry's parents (Allie's posts) did was smart. Teenagers are a pain in the @ss, and every once and a while, they'll need a repeat reality smack in the face. If you can provide that, it'll probably do worlds of good.
The only other thing I wish to add is: Don't nag. It seriously will get you nowhere. This is going to horrify some parents to think about, but in high school, I smoked pot. Yes, smoked. Brownies are terribly difficult to come by. It wasn't every day, I wasn't one of <i>those</i> kids. It was at things like parties, gatherings, etc. But it was still more often than I should have, by a long shot. My parents knew. They didn't nag. I can only guess how hard that must've been. Actually, my parents never even gave me the "If you want to die, that's your business" speech. I just figured it out and stopped on my own. But if you say things about particular stuff like not smoking, that will only make them want to more. "CF can't tell me what to do, and neither can you, mom!" *runs out to smoke 10 joints* You get the idea. Hahaha.
I'd say the way you're going is most certainly the right direction. All you really have to do is add to it (maybe become a little more direct/dramatic as they get older "If you don't do your meds, you will die much sooner. If that's what you want, that's your decision, but there will be no one to blame but yourself" much like what Ry's parents said) as they get older. Teenagers really are a pain in the butt. Bigtime. For me, I was worst between 15 and 17. Heh. But then I figured it out. And now I'm with someone who matters very much to me and he won't let me skip my stuff. Somehow, "Do your meds, damnit!" coming from my fiance is much more compelling than when it comes from my parents. Hahaha. <img src="i/expressions/face-icon-small-smile.gif" border="0">