"My powers of memory, Marian, are not like yours. But I was so strongly impressed, so deeply interested, that nothing of any importance can possibly have escaped me." (18.104.22.168)
Laura ties together memory and power here. That may seem like an odd sort of power to have, but most of the book's scenes of power revolve around mental power: the ability to manipulate, to control, to convince, to remember, etc.