The general consensus on this is that alcoholics must cure themselves. But it's not black and white either. I cured myself, but I had to reach out to others to do that. OK, OK reaching out is something I had to do by myself and on my own, so you can maybe argue that it is still up to the alcoholic.
A few years ago, holding interventions were all the rage. It even became a Hollywood Movie cliche'. I haven't heard much about them any more, so I'm guessing they weren't all that effective, but we don't know that either, because if there is any sociological data to support interventions as a cure, it is not widely published. We don't actually know if holding a family intervention is going to work.
This is not to say, it's not worth a try. The fact is we have little data supporting any particular program or method that gets people sober. All we know is that is that any of the common methods work... if only sometimes, and that most recovered alcoholics do it entirely on their own.
I would talk to your sister about her drinking. Be honest with her about what she is doing to herself and her family. Do it without worrying too much about if you are doing it right. Just understand that she is not intentionally an alcoholic, but that getting well is possible if she wants it. But know that what you can do is very limited.