Best not to say anything or stir up anything... especially before leaving for you new job.
I would not say anything.
I assume you already got your references/recommendation letters, to keep for your files in the future.
If you know she is drinking, then others probably know too, and she probably smells of alcohol too.
But still, you are leaving for a new job, and I would just not say anything lest you create "problems".... which would reflect upon you, before you leave. You want to leave with a good impression, (even though you already got a new job), so that the "company" views you positively and you are leaving on good terms.
All the best,
Susan