Rebelmom, I am sorry about your daughter. I have one who I enabled badly way until her 30s. Sounds as if your daughter may also be near 30.
There comes a time when I feel it is best for our struggling kids if we just back off and refuse help. Why be nervous because she wants to live with you? Tell her no. No is a complete sentence. Sounds like she is doing drugs. Your home is a sanctuary for you. You are not being mean by protecting yourself and your other kids. We had to do the same. It took us about 12 years too.
I highly recommend finding a good therapist whom you like (interview a few before picking one) and going to Al Anon or Nar Anon. Nothing says support like people who truly understand your situation. It really helped us! We used both. Our therapist specializes in drug users and has been very helpful.
Al Anon is great. But you are advised to try it six times before deciding it's not for you. Al Anon, and the friends we made, are still invaluable.
Church or any place of worship can also help. Our church family is like a caring family.
Don't try to do this alone. in my opinion it's just too hard to not be in touch with people who truly understand us.
Prayers and blessings. Nothing changes if we don't change us.