James said:
I believe he's referring to interviews Allen gave for KOTCS. She mentioned discussing the character with Shia, and downplayed any notions that Marion had been an alcoholic.
That's the one. I didn't manage to come up with the exact quote, so I guess it came out a bit fuzzy as a result.
And James, I'd say that you're quite right that it was a vice born of necessity, but that doesn't mean it would have disappeared eventually, at least not without effort. After all, she was left at the altar and discovered she was pregnant shortly afterwards; back then, it was probably felt on some instinctual level that a drunk pregnant woman was a bad idea, but not due to any science. Then she lost her husband in the war, when her son would have been no older than 7 or 8. That's some stress, with Oxley in the picture or not.
So, yeah, maybe she quit, but I'd guess that it would have been from active effort rather than just losing the taste for the stuff.
(And all that's to say that she's actually an alcoholic, not just an occasional-to-frequent heavy drinker without quite so much compulsion.)