It's not unusual for a parent to feel this way.
This is the son she gave birth to, raised, reared, taught everything she knows.
And now he's an alchoholic, who nearly destroyed his life.
For her, she probably feels she's the ultimate failure. His sickness and failures in life reflect on her. She's probably thinking;
He can't be an alchoholic! What kind of mother would I be to raise an alchoholic! He's just...sensitive! It must be her (your) fault! Besides, I drink! I've drunk with him! And I CAN'T be an alchoholic!"
See where this is going? I don't know if you can do this, but if you can try to make her see that his problem doesn't mean she's failed as a mother (I'm NOT saying this is true, by the way) then maybe she can come to terms with all this.
There's also the fear that she may be an alchoholic as well. Alot of people who drink socially (alchoholic or not) feel uneasy around recovering alchoholics. It makes them look at their own drinking in a way they'd rather not.
I think this is the main reason people like her give recovering alchoholics alchohol. They want to *show* them that they aren't alchoholics, that they can handle it, and by association, that means they aren't too. This is especially true in her case. By getting him to drink, she's trying to *force him* to prove he isn't an alchoholic, and therefore, she isn't a failure as a mother.
I hope this helps, whether or not it fits what's going on. It may not make her easier to deal with, but understanding a person's fears can go along way towards forgiving them their behaviors, and bringing peace to your own soul.