Don't put her in rehab, that's stupid. Marijuana has no addictive properties, at least not physical addiction. She may feel a phsychological addiction, but that's not cause for rehab. It's probably a phase. I went through it too, smoking weed everyday, eventually it got old. She'll probably grow out of it. But just in case, I would say, punish her and I mean REALLY punish her. My mom let me do whatever the hell I wanted, she would find a bag of weed in my room (sometimes worse than weed) and she would simply confront me, say don't do it, then let me be. Then I would go smoke more cuz I knew if she found out she wouldn't do anything but scold me. She never grounded me, or gave me any discipline at all. She gave me plenty of love, as is obnvious that you do to your daughter, but be sure to discipline her, cuz if you don't she'll think she can do whatever and you'll be fine with it.

It's a tad trickier since she's 18. I would say evict her, or at least threaten to, if she doesn't quit. Give her tough love. If she's still in high school, it'll be easier to ground her and stuff like that. If she's in college, threaten to stop paying tuition. As I said before, tough love.