Well, if we're going to use Wikipedia references:
https://en.wiktionary.org/wiki/queendom
Besides, there have absolutely been monarchy-type governments ruled by women. Some, like the UK, still have men as the norm and only see queens as head of state under very specific circumstances. Others have actually been matriarchal. And I imagine there have been all kinds of hybrids since every culture has a slightly different idea of gender roles and inheritance. Is the "queendom" a commonplace word used to describe them? Not really. Does it serve its purpose in game by providing an extra little immersion for monarchies with female leaders? I think so. And it's a has a pretty intuitive meaning to it.