The "big frikkin' deal" is if you didn't already have a list of rules conspicuously posted -- then it becomes awkward. I agree it's common sense not to train in makeup -- or with anything other than very short nails, or while wearing jewelry of any kind, or in an unwashed gi. But I've said it before and I'll say it again, people in the US are going to think of a dojo as being like a gym, and people do all those things at a gym. If you've ever been in a gym and seen the way some women get all chicked out to work out, you should know that there's a cultural thing. Working with it seems like the sensible thing.
I think that the point is that it's not a big deal to discuss the situation with the student in a respectful fashion irrespective of published rules etc.
It might make one consider publishing such rules/guidelines for future reference but a polite discussion with a student shouldn't be a problem in my opinion.
I've had several discussions about appropriateness of clothing, removal of jewlery etc on numerous occasions with new starters and never had one take umbrage; maybe they were all outraged but too "British" to make a fuss though