Hi! I believe I can be of help with this issue.
First, let me say that from the clarity of your writing and your ability to convey the information comprehensively, you are certainly the clearheaded adult in this situation and you care for and love your granddaughter. This is very beautiful and very important for her but it is also a bit heartbreaking for you. Because your concern for her safety and her wellbeing are extremely well founded. And your question for me is what you can do about it and I sense that in your heart you know that my honest answer can only be that there is very little DIRECT action you can take to make things better. That it all depends on her now. She's an adult legally. Her parents have little they can do, though it sounds from the situation in the family as though their dysfunction compounds the problem for your GD.
And this is actually the key to my answer to you that you need to consider and think about. She has clearly never been able to rely on her parents for order and orderliness in life, that she needed to create her moral behavior compass in other ways. And she had difficulties in doing this and couldn't find the direction to take that would lead her out of "dysfunction mode" and so she has sunk deeper and deeper into it. As has her sister.
So you have to continue being there for her offering love and encouragement. Don't minimize this! You can't directly make her change course. And she does not need to be told how she's messing up by the people who love her. She knows. But she needs to be told over and over that there is hope, that if she keeps trying, she will find a handhold to pull herself up. And this is the message I strongly urge you to keep exuding and sending. And the message has to include practical encouragement.
I consider Alcoholics Anonymous the most important resource a person like her has available to them. There's a reason they're still around after 80 years: they know what it's like to feel pain and discouragement at 2:30 am and they have the sponsors there that will talk to her then or any other time. And it takes that kind of support.
Here is the web address for finding a meeting. Not all meetings are the same. So if she doesn't like the first one she goes to, tell her to go back to the office and ask for a different meeting she can try:
Now, I'm looking at the directory for Japan and all I see is a web address for AA in Tokyo as the central location for information for other areas of Japan:
I also want to give you the address for Al Anon. That's the part of AA for families, to give them support and strategies for not enabling her. I don't sense from your writing that her parents would go, but it would be so beneficial for them just in their own dysfunctional behavior because it would expose them to what dysfunction can wreak on people in families. So if they will go, here's their meeting finder:
You may want to consider going for yourself, the support may be comforting for you and you may make friends there and possibly some ideas for dealing with your family. But you seem to have found your way to deal with all of them. So my main concern is really your specific question about helping your GD.
I have seen enough people to tell you that from her history it is clear she knows how far down the wrong road she's already gone and continuing to go. That's not her issue. Her issue is feeling like she's not worth going down any OTHER road and so just numbing herself with drugs and alcohol. So please believe that being a voice of encouragement and loving kindness to try to get support to help herself, to help herself get help are all so vital.
I wish you the very best!
Please remember to click the green accept button. Feel free to continue the discussion; my goal is to get you the best answers possible. Bonuses are always appreciated! If I can be of further help with any issue, just put "for Dr. Mark" in the front of your new question, and I'll be the one to answer it. All the best, XXXXX XXXXX