Who is Uncle's Wife from Woman at Point Zero and what is their importance?

Firdaus' uncle marries the daughter of his teacher at El Azhar. His wife is a short, fat woman with a fair complexion, and her voice has a softness born of cruelty. Her eyes are large and black with extinguished vitality that leaves pools of dark, sleepy indifference. She objects to having sex with her husband because it is sinful, and she convinces her husband to send Firdaus to boarding school and to marry Sheikh Mahmoud.