Lila Prasad, 62, died Sunday at Seton Medical Center in Daly City.
Prasad and her grandson were found unconscious when firefighters responded to their burning home in the 100 block of Lake Drive at 8:45 a.m. Friday, Deputy Chief Dave Downing said.
The woman was revived and taken to the hospital, Downing said. The boy, Aakash Prasad, was declared dead at the scene.
The cause of the two-alarm fire, which was extinguished in about 15 minutes, remains under investigation, though authorities believe it likely started in a shrine that had been set up in a hallway closet, Downing said.
The flames apparently blocked the woman and her grandson from evacuating.
A 69-year-old man whom a neighbor identified as the boy's grandfather was hospitalized with burns.
Funeral services for Lila and Aakash Prasad will be held Friday at 10 a.m. at Chapel of the Highlands, located at 194 Millwood Drive in Millbrae.