Hi Grammy,
I can tell you've got good instincts. I've known a lot of people that have gotten messed up pretty deeply into their children's addictions before seeking help. I'm impressed that you've been able to see things so clearly in a relatively short time. But that doesn't make it any easier, does it?
I know a lot of people have mentioned that you may want to attend an Alanon meeting, and I would like to second that. Mainly because I meet a lot ( a LOT!) of people that are there because of their adult children. I'm not sure if this is common to most Alanon groups, or just mine (mine meets in the middle of the afternoon), but it's at least 60% men and women who are dealing with exactly what you're dealing with. Of course, we all gain support from each other, but the unique understanding these parents all have can't be overstated.
My heart goes out to you. You, you're GD, and you're daughter as well will be in my thoughts and prayers. Believe it or not, the best thing you can do for your daughter is exactly what you're doing right now, seeking help for yourself.