Joanna Lannister
From Asoiaf
Lady Joanna of House Lannister was the sister Ser Stafford Lannister. She was married to her cousin Tywin Lannister, Lord of Casterly Rock. She died in childbed. They had three children, Ser Jaime of the Kingsguard, Cersei, married to King Robert Baratheon, and Tyrion.