I don’t even feel sorry for Mary. She seems to use her mom’s death and impotency to fish for pity or show off her comedic side (in which case she would be kind of bragging). In conclusion… Fuck you, Mary, nobody cares.
Sure, barren is probably a more correct word. However, impotence is the quality of being impotent. Impotent means “unable” or “lacks the ability”. Hence, women can be impotent. Also, since the topic is obvious, “impotent *of having children*”, the *xxx* part is not needed.
BTW: if she indeed tried to be funny, she should try harder.