I think there's probably another step in here. It's not that being a girl is degrading. It's that being a girl is weak (and all the things that come with weakness, whether it's using manipulation instead of force to get your way or submission), and being weak is degrading. And a step further from that, even--feminized insults in English stop being about "women" or "girls" at all and only about what that femininity means. And until femininity changes from being subordinate and inferior, they won't stop meaning that, and it's useless to point to the language to try to create that change, because language doesn't change anything.