Even though I'm generally a "rule guy", I'm with Barto on this one. There are ways of driving the right behavior without making her feel like a piece of shit, and otherwise calling her out for probably doing her job really well (i.e. being attentive to the patron, creating a pseudo-bond while the patron is in the restaurant, etc.)
As someone who now doesn't look even spitting distance from 21 - my SHIRTS don't even look under 21 - I, too, get a little bugged by the "we card everyone" nonsense. I get that the fines are significant, and if I stroll in to a bar within walking distance of a college campus with 20 people of varying ages, sure, but traveling for work, I often drink alone - that didn't come out right - and I doubt that Johnny PoPo is staging a vice raid because I got a Tito's and soda from a hotel bar in Rochester, NY without being carded.