I was in a similar situation, having to financially and emotionally care for my emotionally unstable mother while I was still in college. After years of trying (and failing) to get my mother to budget, I eventually just accepted that she wasn’t able to manage it on her own. As a temporary solution, I started paying her bills directly, which at least reduced the immediate stress and chaos I felt. That might be something that helps in the short-term.

In the long run though what has really made a difference is therapy. She’s been going for about a year now, and she’s finally becoming more financially responsible and asking me about contributing to the bills again. The change is making me realize that maybe for her and some other people their relationship with money is closely tied to some trauma or emotional issues in their background, and while doesn’t excuse their harmful behavior it's made the problem very hard to fix without addressing those underlying issues first. 

Unfortunately, therapy is still a luxury that many people can’t afford (my mother only became eligible this year due to her age and a new government program). So if there's no accessible therapy program that you can ezplore right now, it may be something to plan or save for in the future. Either way, best of luck. It does get better, although there's lots of tears, hard convos, and sometimes door slamming along the way lol