Mother Superior Mary Mary is the head of the Sisters of the Divine Magnatum, the nunnery that Olive runs away to. She appeared in "Bzzzzzzzz!", "Circus, Circus", "Window Dressed to Kill", and had a larger role in "Bad Habits".
She provided shelter to Olive after she was dropped off by former fellow nun Lily. Because Lily had entered the convent to hide a pregnancy, initially Mary Mary believed Olive was there for the same reason. Shortly after realizing her error, Mother Superior began to establish Olive within the convent, by helping give all of Olive's belongings to the poor.
Over the next few weeks, she kept a close eye on Olive, making sure that the new arrival attended the frequent prayers held at the convent.
Later, Mary Mary would be implicated in the suspicious death of fellow nun, Sister Larue, who fell to her death from the belfry. Emerson Cod and his team, hired by Olive, revealed that Mother Superior had discovered an affair that Larue was having with a local chef, and ended it by leaving a forged note and sealing up the secret corridor between the convent and the restaurant. Mary Mary would also be the first to figure out that the team claiming to be the Vatican Secret Police were fakes, after she talked to Charlotte Charles about her uncertainties concerning God and her faith.
It is ultimately revealed that Sister Larue was knocked out of the Bell tower by Pigby, the truffle hunting pig, after discovering Larue's secret white truffle-making lab in the tower. Olive tells her friends as she leaves the nunnery that Mother Superior planned to continue Larue's work.
Later, in "Window Dressed to Kill", Mother Superior makes a final cameo with the Sisters of the Divine Magnatum, at the request of Olive Snook, to assist the waitress' former "kidnappers" Jerry Holmes and Roy "Buster" Bustamante in crossing the border and evading capture.