Oh Paul, sounds awful for you. My husband was using coke and diazepam, I know what you are going through.
Redfox is right, its guilt pure and simple. She does need professional help, but until she’s ready to accept it, the thought of it probably terrifies her. The existence she has at the moment she thinks is acceptable, she can function to an extent.
Do her family not know? My husbands dont/didnt, but they must see the difference now that he’s clean. They probably wouldnt have ever thought drugs, but they may have thought drink.
You need to look after yourself, she is not your problem, you didnt get her into this, and you can’t get her out of it. She has to want to, and i’m not sure shes there yet.
Take care of you.