I mean, I know that several decades ago women's pants tended to have a zipper on the hip rather than at the fly, and an extra high waist. These days, the big difference seems to be that they are shorter in the leg and hug the crotch and butt way more than men's pants do. I know that personally I have never been able to successfully wear women's pants comfortably, whereas men's pants fit just right.
Anyway, unless there are other locations where they sometimes have women in skirts, this rule seems pretty ridiculous. It sounds more like something your friend is glomming onto, rather than anything management is going to enforce. What are they going to do, exclaim, "Those pants aren't ass-shaming enough, they must be GUY PANTS" and write up a citation?