Who comes to Martha Boyle's doorstep at the beginning of the book, and what does she want?

The novel opens with a woman knocking on the front door of Martha's home. The woman introduces herself as Olive Barstow's mother. Olive was in Martha's class at school but had been hit by a car while riding her bicycle and died only a few months earlier. Olive's mother tells Martha that she'd found a page in Olive's journal that she thought Martha should have. She hands Martha the page, says "thank you" to Martha, then leaves.