Who is Sister Mary Praise from Cutting for Stone and what is their importance?

Sister Mary Praise is Shiva and Marion's sister. At the start of the novel, Sister Mary is a nun sent to Africa to fulfill her nursing duties. On her journey, she is raped in Aden, after which, she makes her way to Missing Hospital where she knows Dr. Stone. For seven years she acts as Stone's assistant, and eventually, he fathers her twins although he does not know of their existence until the day they are born. The trauma of the delivery kills Sister Mary Praise and forever devastates Dr. Stone.