She's still at school? Who cares? She's young enough that she will learn sooner or later. If she were 30 and doing this stuff I'd say something. As it is, let her make her own decisions. To be perfectly honest it's none of your business. How is she supposed to learn the ins and outs of relationships if you control what she does in them? If her talking to you about it annoys you so much, svck it up and ignore it when she starts talking. "Really?!", "No! He's terrible!" and "You deserve better" are good lines to keep to hand when you realise she's stopped talking and is waiting for you to respond. That's what most men do to most women anyway.
It's really not your business. After she breaks up with him and before she starts dating someone else, you may be able to have a discussion with her, but now is not the appropriate time to say something. And what does the guy's nationality have to do with any of this?