RORY: But … what’s wrong with her [Madeline]?
LOUISE: Nothing’s wrong with her, Mary.
RORY: Mary? Oh no, not this Virgin Mary thing again.
LOUISE: Not Virgin. Typhoid.
Typhoid Mary was the name given to the Irish-born American Mary Mallon (1869-1938), the first identified person in the United States to be a carrier of typhoid fever without displaying any symptoms. She is believed to have infected an estimated 51 people, at least three of whom died, while working as a cook. As she used fake identities and was able to give authorities the slip several times, the numbers could be far higher, with some estimating that she may have killed over 50 people.
Mary spent the last 23 years of her life in forced quarantine, as she refused to stop working as a cook, even after being told she was a carrier of disease – she would not accept it. Typhoid Mary is a name given to anyone who unknowingly spreads disease or other undesirable traits.
Louise means that they intend to “quarantine” Rory by ignoring her, showing that she and Madeline are loyal to Paris, even when she is being unfair.