I wonder what the response would have been had the cashier used the "N" word or some such.
Bad idea: Don't require your cashiers to ask for that name. This is not an unexpected outcome when your entire advertising structure is dependent on the judgement of an army of minimum-wage minors.
"We're all of different races here in this store. So she didn't mean any harm, didn't mean to stereotype against her, to discriminate against her, but that's how she took it." With talent like that, any one of a million situations popping up that require judgement that training doesn't cover are going to put you at risk. I guess you get what you pay for.
-That's how she took it? As if her perception of the event was the problem?! Oh papa!
If anyone expects a 17 year old to have a sophisticated well balanced idea of correct workplace behavior they are out of their minds. I'd feel bad for the girl if she wasn't learning an important lesson.