Why not just say 'woman'?
^^This, completely (except 'female' would probably be better, as the menarche almost always occurs before reaching adulthood).
I imagine the advertisers' planning meeting went something like this:
"Let's say 'the average woman' uses this many products...."
"But what about transmen? We don't want to offend them."
"But a transman is a biological female - genetically a woman - so they'll know that this obviously includes them - at least until or unless they commence radical hormone treatment and/or have a hysterectomy in their quest to identify as men, which they have every right to do. They'll have no reason to be offended or complain for the sake of it."
"Ah, yes, but we'd better not risk any bad press. Well, then, to make sure that we don't offend any transmen, we'll add 'menstruating' - 'the average MENSTRUATING woman' - just to underline beyond any doubt that menstruating is the whole purpose of what we're discussing here: if you menstruate, this advert might be of interest to you."
"Ah, but what about transwomen?"
"Well, that one's easy! A transwoman is a biological male, so whatever they do or don't seek to alter, they will never menstruate. They will obviously know that this advert isn't aimed at or relevant to them. They'll just see it's about periods, ignore it and move right on to the next advert or article. Nothing to interest them, much less offend them."
"But some of them CAN be very vocal and seek to complain about perceived problems, where none actually exist. Even though what we're saying has no relevance to them, they might still decide that everything should primarily be about them and complain bitterly about us. They could throw accusations like 'transphobic' and 'discrimination' at us. Transwomen activists can be very vocal and seek to destroy anybody who disagrees with them."
"Ooh, OK, then. Well, we'll change it from 'menstruating woman' to just 'person', then. 'The average person uses this many period-related products in their life'. All good."
"But that isn't true. 'Person' includes males. Males obviously don't use any of these products at all - ever. And 99.99% of males would accept this as common sense and would see it as absurd to quibble the fact or venture to offer an opinion as they know it's clearly nothing at all to do with them. They really couldn't care less."
"Hmm. Right, then. So we need to appeal to all people, but make sure they know we're talking about menstruating. Let's just go with 'Menstruating PEOPLE,' then."
"But that's absolutely crazy. Everybody knows that only biological females menstruate and that virtually all females will menstruate for many years of their lives. Menstruating = a female concern. Everybody knows that. We don't want to risk offending women by glibly homogenising a very significant part of their lives with men and making it look like it's somehow shameful or sexist to specifically refer to 'women' when addressing female-only concerns."
"Well, we WON'T offend them. Not all women, anyway - transwomen will be happy and agree with how we've carefully included everybody and made sure that they don't feel marginalised. Invariably, there will be some women who are offended, but it won't be all women - only maybe some of those ciswomen. At least transwomen won't feel excluded."
"But transwomen are biologically male. We're talking about menstruating, so, by nature, they - along with all males - are, by definition, excluded!"
"Excellent - I'm so glad we all agree. Inclusivity it is, then - we'll write 'menstruating people'. That way, absolutely nobody has cause to be offended and, if they are, well, they must have personal issues. That's their problem and not ours. Perfect: all sorted!"