Meredith Rodney McKay's mother is a female Tau'ri, the wife of Meredith Rodney McKay's father, the mother of Dr. Meredith Rodney McKay and Jean Miller and the maternal grandmother of Madison Miller.
She and her husband constantly argued during their son's childhood and blamed Rodney for it. They eventually divorced. (SG1: "Redemption, Part 2")
In 2004, Rodney told Dr. Carson Beckett and Lt. Aiden Ford that his sister was the only family that he really had, implying that both of his parents had died by then. (SGA: "Hot Zone")
While suffering from Second Childhood in 2008, Rodney could barely remember her. (SGA: "The Shrine")