Families & Friends Of Addicts Support Group

I'm sorry to hear what you're going through. It's not easy loving a drug addict...
Unfortunately there isn;t much you can do for her. Of course she only talks to the people who smoke with her. That's her comfort zone. Anything that's between and her drugs has to go.
I was a heavy pot smoker myself and I loved doing so much, that I stopped going out, stopped hanging out with my sober friends. In the beginning I only hung out only with my friends who smoked and slowly I even stopped doing that... I just wanted to be home alone by myself and smoke as much as I wanted and just pass out. And people try to tell that I had a problem, but I didnt believe them... I only stopped when I became so miserable and the pain got so great, that I just wanted to die. So I seeked help.
She's mody because the pot is messing her up. Some people think that smoking pot is not a big deal... well it is. Especially if you do it often. It affects your mood badly. Basically, when you're not stoned, you're miserable, you can;t hande life on life's terms anymore, you can't sleep, you lose some of your short term memory.. I was even hearing things toward the end.
I am telling you this so that you can understand where she's coming from. Don't take it personal, this is a disease and her behaviour has nothing to do with her love for you. It's just sickness.
However, this disease is hurting you too... The best way to learn how to deal with it is by going to Alanon. I think it'a great that you dont' want to be around drugs. Good for you.
You can only take care of yourself. She has to make your own decisions. Even though you are her older sister, you are not responsible for her and her actions. We all have the ability to be responsible and to take care of ourselves. It's just a matter if we do it or not.
Try a few Alanon meetings. You will find a low of answers there. And keep coming back here. We all understand what you are going through. Hugs...