Just because one might say something about a man, or men, does not axiomatically mean it is not sexist to make a similar observation about a woman, or women.
If you acknowledge that there is institutional inequality in our culture, that should not be a difficult concept to understand.
There are narratives, stereotypes, concepts, even individual words that have entirely different meanings, and evoke entirely different reactions, when applied to men and when applied to women.
We don't say things like "zie trades on hir appearance" in a void. We say them in a culture steeped in gender inequalities, one of the most basic being that women are judged on their appearance in ways that men are not.
That doesn't mean it's not allowed, or impossible, to speak about female public figures who simultaneously benefit from lingering anti-feminist tropes and the feminist activism that has afforded them the public platform from which express their privileged disdain.
It just means that discussion has to have some nuance, has to be more thoughtful than "bitch trades on her looks." And it is not defensible with some offhand fauxquivalence like, "I'd say the same about Mitt Romney," when we all know that no one does say the same about Mitt Romney.
And even on the rare occasions male politicians are accused of trading on their appearance, guess what? It's done under the auspices of calling them girly.
Yeah, it's a pain in the ass to constantly be aware of marginalizing tropes, but, in moments when you may be inclined to feel a harrumph of unfairness, consider that I would happily give up 80 biebillion fucktons of institutional misogyny in exchange for your right to say whatever the fuck you wanted without having to take two seconds to think about it first.