(((kitten))) - I'm so sorry you are going through this. I'm an RA (recovering addict) and have loved ones who are still A's (addicts).
As far as letting your daughter live at home? If my family had done that, this is what I would have felt:
1. I would have lost respect for my family, that they allowed me to do whatever I wanted to do, and gave me a safe place to do it.
2. I wouldn't have had those glimpses of how they went on with their lives, despite what I was doing. Eventually, I saw that and wanted to BE a part of their lives again.
3. I wouldn't have had to deal with the consequences of my using, which is why I eventually chose recovery.
I'm waaaaay older than your daughter, but addiction sucks, no matter what the age. I came close to death, more than a few times. I was locked up, lost everything and am still dealing with the career/financial/legal fall-out of my poor choices, almost 5 years later. My xbf continued using crack (our DOC) and died.
However, I will always be grateful to the people who loved me enough to let me find my own way to recovery. I did the prostitution, I did the living-in-one-crack-place-to-another and I lived on the streets. I see my niece, the same age as your daughter, heading down a similar path, though it is with alcohol. I can't stop it, I can't fix it. The best I can do is show her how life can be WITHOUT the stuff, set boundaries of what I will, and won't tolerate, and pray that she gets it before it's too late.
Hugs and prayers,
Amy