Kathy, my heart goes out to you. Your difficult child is really upping the ante here. I would agree that she sounds borderline, to a T. I think I've probably passed this on to you before, but this book in particular helped me undertand more about the disorder and helped me put my own thoughts in perspective:
http://www.amazon.com/Essential-Family-Borderline-Personality-Disorder/dp/1592853633
It's a sequel to the original "Stop Walking On Eggshells," which I've also read, but I found this one even more helpful. Heck I'll send you my copy if it will help, just PM me your address.
I think you are doing everything you can at this point, and actually think you are doing a great job at detaching. She's upping the ante because you are cutting her off, and she can't stand it. This is pretty typical of Borderline (BPD). One of the behaviors on the DSM is: " Frantic efforts to avoid real or imagined abandonment." She's got that one down pat, doesn't she?
As for Al-Anon, I think it's an awesome organization, and their core principles are important. I think it can be a wonderful support group, and has helped a lot of people cope. I always encourage people to attend. That being said, having been to many meetings back in the day, they're all different. Some helped me a bit, some didn't help me at all. I think I went to 3 or 4 different meetings/locations before I found one where I felt comfortable. So, I urge people to try several before giving up. But, in some areas, that's not an option, and even if it is, it's conceivable that you could go to 6 different meetings and never find a group of people that you "click" with. So I also get why people have said it doesn't work for them. It's very personal. Just like therapists... I feel SO lucky to have found one that I "click" with and that I love.. I couldn't do this without her. But many people search and search and never find one that works for them. I do think it's worthwhile picking up some of the Al-Anon literature to read, especially their daily meditation books.. I used those more than I went to the meetings, actually. Might be worth going to a meeting just to pick those up. Bottom line is, Al-Anon is just another potential tool in your detachment arsenal. It's not the only one, and it's not for everyone.
Hang in there.. I'm thinking of you. Our difficult children are alike in many ways.