She took one Monday off because she was going to a rock concert on Sunday and announced she'd be too hung over to come to work the next day.
Mommy's little girl was shocked to find out that, as a summer intern, she wasn't entitled to a paid vacation day to nurse her hangover.
America's future.
Well, I'd have no problem with her taking a day off because she's too hungover to work. In fact, having come in after a few late nights myself (in my wilder years...) I'd rather not see her at work.
But, as an intern, you miss work, you don't get paid. Actions have consequences. lol!
I think this was a good time for your intern to learn this particular lesson. Better now, than after college at a fulltime job where it really counts and your rent/food/etc is hanging on it.