Caught up! Sorry, double-posting.
I have read that menstruation is actually something much more common now than it has been for much of history. I agree it's partly because badly-nourished women don't have periods (though I think that's very plausible - there's a thing called 'greensickness' which the Early Moderns thought teenage girls got, which is basically anemia, as far as I can tell - they were presumably menstruating and losing iron, and you 'controlled' it by diet, presumably by stopping periods). Looking at diets for, say, certain nuns, it'd be surprising if they were well enough to menstruate.
But also, married women would likely be pregnant quite a lot. We know in some times women would miscarry time after time - you might not associate a woman losing blood with fertility at all, but the opposite. And although some women were married at 14 or earlier, it seems they didn't usually start periods as early as we do.
I'm rambling, but I do think it's understandable if people didn't recognize periods as regular and therefore 'normal'. I've also heard the Elizabethans thought you were most fertile during your period - but I think they also had a very different sense of fertility than we do (they can't have assumed it was just those few days or they'd surely have worked it out pretty soon!).
I don't to be honest buy either the idea that earlier societies would necessarily believe women's periods were a sign of power (not regular enough, etc.), or that they'd necessarily think it was horribly unnatural that women 'bleed but don't die'. There are ancient taboos about menstruation, but my impression is that English-speaking society today is much more disgusted by it than it has been for the last few hundred years, certainly more vocally disgusted. It's one of the favourite arguments about why women are 'dirty' and need to become paranoid about their bodies in order to avoid being 'dirty'.