" . . .when I hear her say "please don't leave me" - my internal filters hear "please don't leave me so I can keep drinking."
^^^ Your internal filter is probably right on this one MC. Yuck.
Do you have a plan of how you are going to proceed from here? It might be good to have a plan for if the rehab takes and a plan for if it doesn't. I suppose the boundary is some action on her part where you do actually leave her. I have no idea what any of this will look like for you.
Trying to be supportive here but I know it must be so ding dang dad blasted difficult and not much that anyone can do. So often on Soberrecovery I feel like Sheldon Cooper in the Big Bang Theory; All I can do is pat you, say "There, there" and offer you a hot bevarage.
For what it is worth here is a group hug: