Martha was a Human woman that lived during the 24th century. Her brother and niece Kathryn were both prominent Starfleet officers.
While Kathryn was growing up, her Aunt Martha told her stories she'd heard from her ancestors of Shannon O'Donnel's work on the early Mars missions and how she fought opposition to build the Millennium Gate. These were an inspiration for Kathryn's and her career in Starfleet.
In 2375, while researching Shannon O'Donnel, Kathryn was disappointed to find that most of the stories her aunt had heard were exaggerated, if not all-together wrong. One question she asked herself was, once they got back to Earth, what would she tell her Aunt Martha. (VOY: "11:59")
This character was only mentioned in dialogue.
Although not specifically noted as being on Captain Janeway's father's side, her knowledge of Janeway genealogy seems to indicate this.
Her surname, according to the Star Trek Encyclopedia, 4th ed., vol. 1, p. 382, was Janeway.