It is what it is, and she will continue to enable him until she's ready to stop.
You know, I bet she thinks something similar about you.
(we don't have a 'raised eyebrow smilie... grin).
She would like YOU to be the tough guy - to "keep her son" from using. So when you actually do the right thing and walk away... she is angry with you, and not her son. Just as you are angry with her, and not her son.
That boy must be quite the charmer! (And since I only fall in love with alcoholic/addicts, I can just imagine!)
I hope you can find a way to forgive her for being so nasty. That hatred and anger is most likely stuff she feels about herself... projected out on you.
I am learning through my step work and working with my Alanon sponsr that for me, the stuff that I see in other folks that grates on me the hardest, are usually my OWN faults.
The alcoholics say it short and sweet... "you spot it, you got it".
And they are right... generally, I do.
None of this may apply to your situation at all... but that is how it works for me. I am glad you are here. Most of us have been in your shoes, or are going through something similar even now.
I wish you the best.