As Elton John says, if you're an addict moderation doesn't work. I was really shocked by that when she said she smokes weed and drinks when that's how the last spiral started. But at the same time I admire her for not hiding it. I don't think she is as at peace as she makes out. Same as you, I can't see a happy ending and when I finished watching it I was like... ok I can expect to see a devastating headline about her.
I knew Amy Winehouse, acquaintances, not best mates or anything and the whole miserable on tour and overdose story reminded me so much of Amy. And you know how her story ended. Demi is very very very lucky to still be here and I hope I'm wrong that dabbling in milder drugs will only lead to harm for her.
I do kind of get where she's coming from, doing things in extremes seems to do her no good and she's trying to find balance but I can't see it ending well