Stop trying to blame yourself. Just stop it. Drugs are awful, there is nothing you can do about that. She has to control her addiction and work a program to do it.
The Three C's:
You did not cause it, You cannot control it, You cannot cure it.
Florida is a hothouse of drug use. She was going to be offered drugs and take someone up on that offer because that would be her decision. She was trying to get drugs. So while you think she was clean, it would not have been long. She has to face her addiction head on.
I am sorry. I know it hurts. I know it's scary. Keep going to therapy it will help you. We here at SR will support you always, and I will remind you when you are trying to ingest this as your fault, that IT IS NOT.
Tight, tight hugs.