If your mom is willing to discuss it, you could try to get her into Al Anon and therapy. Aside from that, I don't see what else you can do.
I'm coming from my own situation where I don't see my mom as a victim of my brother; I see them both in a sick relationship of mutual destruction. But like I said, my mom has really enabled my brother his entire life. There might be more hope for your mom; I don't mean to sound so pessimistic about the whole thing. However the bottom line remains: it is not your job to fix it.
And my mom has high BP too..