I have learned from experience to stay out of situations like this.
They know they have a problem They are addicts right? So they know what to do to make it better.
Getting too involved can bring us to a point of exhaustion and before you know it, you're angry, irratable and hate dealing with this person. Drugs ruin friendships. It's a shame.
Start setting your boundaries now and let Mary help herself. AA meetings are in every city so there is no excuse for her if she is really wanting help.
You see, if she isn't seeking a life without drugs, she isn't going to change. She might drag you down with her.
I know about this because of a dearest friend that went through the most horrid drug situation and is now in jail because of it.
She is college educated, bright funny and a loving wonderful friend. Problem is when she started drinking and coming in late, I got stuck with her work.
Then, I started to resent her.
I won't let that happen to me again. She is now in jail. How very sad. But, I have backed away refusing to be part of her life until she is in active recovery.
This protects ME.
Good luck to you and I hope things get better for you.