A elderly native Irish woman, she grew up during a period of Irish history known as The Troubles. Her husband Sean was a member of the the Provisional Irish Republican Army, known as "The Provos" or simply the "IRA." Many years before the start of the series, Sean was killed by the UVF. Though now living in Arizona, the events left Mrs. MacDonagh with a deep-seated hatred of the British.
Mrs. MacDonagh is a devoted Catholic, attending Mass every Sunday. She also likes to drink whiskey in the afternoon and before church, as she finds it makes mass less dull.
Atticus is shown to be very fond of Mrs. MacDonagh, often doing chores around her house and sharing long conversations with her over whiskey. For most of the time he knew her, she was unaware of his true nature, simply believing him to be a kind young Irish-American college kid.
The widow get's her first hint that Atticus is more than he seems when he kills Bres in her front yard. Initially she is afraid that he is a murderer and will kill her as well, but Atticus is able to convince her it was self-defense and lies by claiming the slain god was British. MacDonagh surprises him by not only accepting this explanation, but allows him to hide the body in her yard. Later when the Tempe Pack are at her home, he is finally forced to reveal his real nature and the hidden truth of the world, that essentially all gods and religions are real and that he is a 2100 year old druid.
During the epilogue of Hammered and elaborated on in Tricked, it is revealed that she died in her bed of natural causes while caring for Oberon during Atticus's adventure in Asgard. Moments after death, her corpse was inhabited by the goddess Hel, who rose up from her bed and continued to care for Oberon but neither spoke, ate or slept. Hel later walks in her decaying body all the way to Kayenta where Atticus was starting a new life and explains what happened, saying MacDonagh did indeed die and her soul passed on to the Christian Heaven as she had wanted.
In an interview, Hearne stated that MacDonagh is based on his late grandmother, and is the only character in his books that he based on a real person.