Reading all the comments (Just to be sure someone had already said it) since you are no longer even able to talk to her -- but those who she still at least 'listens to, such as your brother -- could one of those contact an addiction counselor and and ask how to go about it; after all it's not the first time someone has behaved this way.

Addiction to, or over-consumption of pretty much any thing or behavior stems from a void in one's life where you feel constantly that something is not right with my life. So it could lead to over-shopping, -gambling, -smoking, -dosing on opioids (yes there's a book by a an author in Columbia Univ (maybe no longer there) who had the title, Drug Use for Adults. (yes caffeine and nicotine are what one can get addicted to) I mention it so that we understand it's the OVER-doing of these that wrecks our lives.

Millions use alcohol but very small number gets addicted. And same is true of others in the list above. The reason we get into the 'OVER'-consumption is I believe to fulfill a genuine need that is unfulfilled such as close friends, or feeling LESS than people around, or some deep shame, or anger, or fear....

So what I was hoping for you that either you or someone equally well aware of the dire situation you are in could consult with an addiction psychologist. Maybe you get recommended a book, movie, u-tube, that can shine on the underlying issue she is trying to grapple with with her over-use of alcohol.

We all want the best life we can have, but it can't be e.g. having most power, money, beauty, charm.... What is a GOOD life is an ancient question. What seems close to a consensus is having our basic needs (food, shelter, security) met but also our need to know and explore. We call it nurturing our curiosity. Another is our need to do what we believe will truly satisfy our authentic self, And need for PLAY, and wonder. As children we all exhibit these.So some excel in science, others arts, or politics....

I am hoping that one-of-you will be able to show her that a lot more enriching life awaits her. So it will take some effort to go from psychologist to a well-wisher who will be patient with her and listen to what is DEEP inside troubling her that has morphed into this facade of alcohol addiction.

Your pain is palpable, as is your determination; it'd be good to know your next steps.