I'm sorry, but if she really did "everything she can to be great" she would figure out a way to stop drinking and being emotionally and verbally abusive.
I grew up with an alcoholic with a temper for a mother who never hit us and I have spent the last 13 years untangling the catastrophic mess that was my self-esteem because of it, and the 12 years before that methodically destroying every good relationship in my life with my learned-at-home codependency.
She won't spiral if you leave. She *may* use your leaving as an excuse to spiral, but that is on her.
I know she isn't a monster. But she is not a healthy relationship partner right now either, and she has a very long way to go before she can be.