You are not doing her any favors if you play into this. Especially with the drinking. Getting your brother involved really was a good idea. But, people with substance issues need to be ready to change. It sounds like she's not ready. She sounds like a classic "user," i.e. manipulative and selfish. There's always underlying mental health issues for someone who uses any substance, but you don't need to be around to fix it. You can't.
I stopped all contact with my aunt, and hence my cousins, because of her mental health issues and her racism. I did it cold turkey. It's sad that it's my mother's sister, but then I think about the way she acted; I don't need that. I only want to be around positive people who don't suck the life out of me.