Nari didn't have a good history with drugs, in fact she was far from it, she had already been put in rehab a few times.
She was sent out of the country to take care of her own affairs and not raise suspicions about how rotten that family was.
As they say, one rotten apple can rot all the fruits in the basket... Only Eunji remained as the apple to be shown to the world in her exuberance and health.
She was the beloved daughter who would bring blessings and prosperity to the Kim family...
Nari wouldn't interfere in the family's wishes, she was also trying to do the best she could.
She stopped using drugs, but replaced it with alcohol addiction.
Compensate one addiction with another, it wasn't supposed to be that way, but that's what happened.
It was truly difficult to live that way, she couldn't remember exactly if there had been a day when she hadn't felt like going completely crazy.
Be sure to read the auxiliary chapter: "Read it! Moon say!"