You can tell her that there were female Japanese warriors throughout history too. I gave some examples throughout this thread. In fact, I am ethnic Han Chinese and I'd personally like to know if she can name anyone off the top of her head without looking it up other than Mulan, Madame Ching, and maybe Princess Pingyang, not that they were the only female warriors but why she thinks female Chinese warriors were a common thing. Mulan might not have been historical even. And Japan had officially recognized 10 separate reign periods by 8 different female emperors (admittedly the last 2 were under very different circumstances and very different time periods compared to the first 6) compared to only 1 in China.

I am not an expert in Chinese social history (or Japanese social history for that matter), but I can tell you that Japanese women enjoyed an amount (what seems to me an unusually high degree for an agraian society) of status and power prior to the Edo period, especially in the Kamakura period and before. Kamakura's law code specifically protects women's property and inheritance rights as well as outline some responsibility for propertied women that put them equal to that of men. And we even have official document recognizing the rights of a woman to inherit a government position (jitō the basic local administrator in charge of collecting taxes and keeping law and order in a village/estate). Even by the Sengoku, by when a lot of the property rights had been lost (less because of changes in law as in theory Kamakura's laws still apply, but more to do with changes in family and inheritance structure) women could hold a large amount of political power and in a few cases were even official head of the clan. See here for more on that.