Addiction truly is a family disease and often there is healing needed beyond the addict himself.
Being in the middle never serves any of us well. I agree that she must do her own healing and decide whether she wants her brother in her life or not. "Not" is an option we all have to respect. I can't honestly say that if this was my brother and I had been through what she has been through that I would want a relationship with him. But it's her cross to bear and her life to sort out.
That said, I would invite everyone to family events (I love Anvilheads take on this, lol) and then let the outcome fall where it may. Show her love, show him love and most of all, love yourself. That's about the best any mama can do.
Hugs