Female infanticide has existed historically, and in China in the present day. In short, when people can only have a very small number of children, they are likely to opt for a son. Nina didn't escape when she could have. If I were a woman who had forcibly had her female children killed and watched others go through the same for half the children they had given birth to, I could not have stayed and I don't think Nina would have either. Even supposing that I was so madly in love with GunnSar as to have stayed, I would not have let the others be captured.
Men have feelings too.
Without women there is no next generation. I've already shown that Pella and Kate had to be among the last of the Seska born from the procreation vaults. If this were true there had to be younger Seska than Kate. So in summation, I think it possible that the Hommiks occasionally practised female infanticide, especially at times of famine or resource shortage. I do not think that they ever practised it universally.