I'd like to hazard a guess that she hasn't travelled extensively outside the US. Or studied history outside of the US.
There are plenty of people around the world who aren't [show piece of paper] who not only know what sex is, but are more than happy to oppress women based on it. There is no gender fluidity in most places in history and where it was there before the [insert piece of paper] colonialists - appeared limited to micro elements of society. And mostly it wasn't there.
I'm interested why these people aren't focusing on the Abrahamic religions, including Christianity, because they've done more to impress gender norms than any colonial power has, whether via the colonial power or "in-house".
What's most ironic is that the whole trans/non-binary movement is inherently colonialist! They want their views imparted on and adopted by everybody else, because they know better than everybody. The only difference is that this coloniser comes via the internet, reaching people across the world. The British, French, German, Italian, Spanish, Portuguese, and Dutch colonial powers couldn't even have dreamt of such international presence!