molerats have non-breeding females… they are less common than the nueter workers, more common than the males. they are infertile (under developed reproductive systems) but if the queen dies the change in the warrens’s pheremone mix causes them to fully mature, with one of them eventually becoming the queen and the others being forced out of the warren, sometimes being able to start new warrens.
some insect species do as well.
i could see the ratkin having similar infertile females, only with an active treatment required to make them mature into fertile individuals (originally would have served as a population control measure, so the abyssal dwarves could control the number of breeding females)