What memory does Paige have about her mother in a recurring dream?

Paige remembers the dream she often had after her son's birth. The dream turns out to be a memory of Paige and her mother. There are water stains on their kitchen ceiling when Paige is little. Paige thinks they look like horses, so Paige's mother says they should color them in; she helps Paige draw a mural across the ceiling. Paige's father paints over the mural a few weeks after her mother's disappearance.