Also, don't criticize her for using drugs with you. Criticize your PAST mistakes maturely and leave it there. She will realise she is included too, but she likley won't admit it.
Just acknowledge your mistakes like a mature adult, acknowledge what you are doing to clean things up and let her know where things are going from there.
Telling others about the drug use before she does is the best way to go. Do it maturely as I outlined above. Don't criticize her at all. Criticize YOUR behaviour and let her find how that includes her on her own.
