I'm trying to get some more specific female minions, right now we have 2: harpy and succubus. There are some female peasants already and the witch. I could add some hero characters, or change the elf lord to elf queen? I'd rather add meaningful female-only characters, instead of just female variations with different tiles.

A female Keeper would be good though, but what would we call her?

I suppose you could use some cool fantasy names for females, although other than the beard I think it would be tricky to distinguish between a female and male keeper!

I would also LOVE a female Keeper! 

I like how the succubus can copulate to spawn more minions. The female/male idea can make it so the other races can copulate too, thus making them able to spawn an endless supply of enemies to kill. Of course, it'll change the winning condition since it'll be annoyingly difficult to chase down individual creatures. Maybe the other races can repopulate based on their own female/male gender ratios and population size? If the king &/or queen dies, then the population size threshold will decrease drastically or just stop copulating altogether. The wandering creatures can then be captured as prisoners and be used for mana farming.

The female/male gender ratios could also determine creature strengths. For example, male dwarfs stronger than female dwarfs, or vice-versa, female elves stronger than male elves, or vice-versa, and humans/lizardmen relatively the same?

For the female/male keeper thing. Instead of creating a bunch of different sprites, maybe you can keep him/her faceless and letting us choose the color of the robe?

For female-only creatures, maybe adding sirens or fairies/nymphs?