Having a tampon fall out of her purse wasn't as bad as when this kid in my school was talking to me at lunch and a teacher walked by, and just as the teacher walked by a condom fell out of his pocket (this was in 6th grade), but anyways, yeah, as all of them have said, it depends on the girl, but most girls have mood swings, and you don't want to piss them off around their period. If you just don't bother her things should be ok, but being open seems like a good idea. Just tell her you're there for her if she needs a shoulder to lean on, because girls can feel really crappy during their periods.
I'm way too high (too high too high)
To be feeling this dry and low
I'm way too tired, I've tried
I'm fired up and ready to roll