Mariela Martinez is Nora Martinez's mother. She suffers from dementia/Alzheimers.
After losing her husband in Argentina, presumably during the 'Dirty War', Mariela raised Nora in a single-parent female-headed household, suffering great financial burden that Nora discovered Mariela kept hidden from her. Mariela eventually developed dementia/Alzheimers and was dutifully cared for by her daughter who owed her her education and career despite hardships.
It appears as though her dementia is to the point where she has forgotten she quit smoking her Morley Brand cigarettes and that her daughter is out of high school. Her husband is also back from the dead (but not as a vampire). When the home she was staying in was attacked by an infected, Nora took her with her away with her to find somewhere safe.
Mariela first appears after Nora visits her in a nursing home, although she is on her last warning because she keeps wandering off. Mariela clearly hates where she lives and wants to return 'home'. She and Nora leave after a Strigoi attacks the home. After the F.B.I arrive at Nora's house, they flee to Setrakian's pawnshop. While the rest go hunting for The Master, she begs for cigarettes, hassling Zach to get her some to which he reluctantly agrees despite the dangers outside. Bolivar infects her after Strigoi led by Eichorst attack the pawnshop. Nora releases her by decapitating her.
In the book Nora and her mother are captured and sent to a Bloodcamp, run by Dr. Everett Barnes who offers to move Nora into his house, with her mother, suggesting she is still alive. When the others come to break her out of the camp, it becomes clear her mother is no longer alive.