Worried about my grown daughter

In April of 1997 our 12 yr old daughter got drunk and was raped by the17 yr old who fed her gin. She changed on a dime. Went from being happy, well-adjusted, achiever, with lots of friends to wanting to be home schooled and not coming out of her bedroom. She than started using alcohol and marijuana to forget what happened to her. We lived in a very small town and it was so ostracizing. Since that day we have tried counseling, moving, treatment. After the move, she was clean and happy for about a month, then started heavier drugs. She became angry, aggressive, self-focused, manipulative. Always picking boyfriends that were alcoholics, into drugs, and/or abusive. She is now 24 yr old and the single mother of a healthy, beautiful 3 yr old daughter. She has a great job she loves. However, she is on methadone, adderal, klonopin, zoloft, some alcohol, and I just found out is still smoking weed. She is super stressed with raising her daughter alone (her boyfriend just moved out, he was not the biological father). Biological father is not involved as he too has many issues...chemical and anger to name two. Our daughter thinks she is handling all the meds fine and the fact that they were all dispensed from clinics feels its okay. She has agreed to see a counselor (that we have to pay for because her insurance won't, although it will pay for her methadone!). I've tried intervention but it never goes all the way through because she guilts me into thinking I'm the one that's crazy. Amidst all this, her father has had a lung transplant ('95) and a kidney transplant ('02) for a genetic disorder. It is so draining to try to keep up the front of being a normal family. My 3 brothers all have normal, non-using, achieving kids so, of course, they can't understand. Bipolar runs in my father's side of our family so I'm pretty sure our daughter may suffer from that too, and it may be another reason why she needs so many crutches. I worry every minute of every day that something will happen to her or our granddaughter. I don't seem capable of knowing my boundaries, when to act, and how to carry thru to the end with intervention. I always start doubting the situation. I have a good marriage, 25 years this Sept.  We also have a son who is 22 who isn't perfect, but doesn't have that addictive personality. I need the support this website offers--thank you for listening. Gayle