Who is Mammy from A Thousand Splendid Suns and what is their importance?

Mammy is Laila's mother. She is described as often depressed and despondent over the absence and later deaths of her sons Ahmad and Noor, who were killed in the war against the Soviets. When the war finally approaches Kabul, she is finally prepared to leave her home, but she and her husband are killed in a rocket attack while packing.