> And the bartender knew she was driving because . . . ? <
A few simple questions would be all that is needed. Just as a few simple questions is all that’s needed to see if a young person is of age to order a drink.
Such questioning would not be foolproof. But it sure would help.
And one more thing. In my state all the liquor stores have a sign on the front door: “If you are visibly intoxicated we cannot serve you.” It doesn’t matter if you’re driving or not. You will not be served, period.
Such a practice should be mandatory for bars as well.
I don’t think there was any question whether she was of age or not.