There's "defeminize" or the more recent "defeminate."

If we take the other meanings of "emasculate":

In the sense of literal castration, there's "oöphorectomy"; in the sense of complete neutering (removal of penis and testicles) there's "spay."

In the sense of weakening or sapping energy... well, the meaning isn't gendered, but the morphology does follow the "male-as-norm" principle. I couldn't find a feminine gendered variation (at least, not in English), but this also doesn't appear to be the meaning that OP is referring to.