I’m worried about cutting her off from rides to meetings or potentially alienating her from our (very small) recovery community.
She is the one responsible through her actions of any alienating and cutting that occurs, not you.
Be completely honest with her, set your boundaries, and stand by them. It might bring home the reality of her actions. We usually don't quit until we have lost all that we can bear to lose and hit our bottoms by doing so. Don't slow her descent to her bottom by enabling her and putting yourself at risk in the process. That would help no one, except the dealer.
The best way to help her is by staying strong and showing her by example. I know it will not be easy and I know it will be hard, but you can do it. The freedom of recovery is worth fighting for. You are worth it. Only she can decide if she is worth it, although she is, she just needs to come that conclusion.