Hi Lost,
You sound like such a wonderful sister!! You will find some great advice here at SR from those who are or have been going through this same nightmare. So post often and read the stickies!
My suggestion is that you try Alanon meetings and perhaps some counseling for yourself to deal with the feelings of being unable to help your sister. We all know how you feel!
But since it sounds like you have such a strong caring family, I think perhaps an intervention, guided by a professional, might be worth trying. I know it would help you by at least knowing you tried everything you could to save her. But please keep in mind, only the addict can save themselves. No matter what you do, it may not be enough and you don't want to enable her addition.
Get your family involved and learn all you can about addiction and intervention. Check out the T.V. show by the same name on A&E. If she decides to enter a good rehab she may find the help she needs and can perhaps even treat the impact of abuse in her early life that may have helped compound her drinking.
But remember, its up to your sister to decide to get better. Many addicts never beat their addiction and their rock bottom can be death. Its a terrible reality we have all had to face.
I wish you the best!