I've got/had young-ish family and friends involved in drugs, theft, prostitution, gangs (bikie), a friend who forfeited the right to supervised visitation with her son so she could get high. Her words, not mine.
Over the years i've learnt that the person in crisis needs to WANT to help themselves, they're highly unlikely to change their ways for/because of anyone else. They need to love themselves enough to say 'no' to the behavioural impulses that get them into trouble. Us on the outside can only encourage them to see it, but ultimately they have to see it for themselves. Its so hard, to stand back and watch and wait. Sometimes, TBH, they don't change in time, but I can honestly say that I always have hope. I've watched the parents of my god-daughters slip into a meth addiction, do all the sick and crazy **** that it leads to, and come out alive and healthy three years later. There were times when we were'nt allowed contact with the girls, particularly because we'd offered to have them stay in our home as opposed to living in a drug den full of needles and pipes.

Continue loving her and telling her you do, continue telling her all the wonderful things about her, do not judge her or her lifestyle as it will only make her defensive to protect it-its hers. Love her unconditionally and be available emotionally.
She won't change overnight, but she will when she's ready too.
All we can do is sit on the sidelines, cheering on the positive things they do, and hopefully one day soon they will play life's game properly, for themselves and for their loved ones.

Peace to your family, and to your DSD, who obviously is struggling to cope with life at the moment.
xx