FYI, it is a mitzva to actually do the action of Keddushin, both for the male and the female (Keddushin 41a).
The Chelkas Mechokek in AHZ 36.1 says the mitzva of the woman is only as a “misayayh” (helper) to the man for him to be M’Kayem the mitzva of P’ru U’rvu. Accordingly, if the woman is incapable of having children, it would seem there is no mitzva to get married.