Mrs. Milligan was a mundane housekeeper whom Magnus Bane hired to look after his apartment in New York in late 70s. Since Magnus was absent unexpectedly longer than expected, which lasted for two years, vampires decided to make his apartment a temporary residence. Most likely unable to get rid of the strange people, Mrs. Milligan was not able to clean the apartment, though she still consistently paid the bills with the money Magnus sent her every month.
References
- The Fall of the Hotel Dumort (first and only mention)