Who is Mom from Extremely Loud and Incredibly Close and what is their importance?

Oskar Schell's protective Mom is a hard-working lawyer, including Saturdays and some Sundays. She and Oskar's Dad are married 12 years before she is widowed in the collapse of the World Trade Center on 11 Sep. 2001. Ever since, she has been more protective, panicky if Oskar is alone, so her mother-in-law across the street watches Oskar after school. On 9/11, Mom receives a phone call from her husband, claiming he has gotten out of the building and is safe.