The Secret Place
She was in the house.
My office at home is off the front hall, and people who came to see me came in the front door past a child on the stairs.
She was, functionally, standing in my lobby for eleven hours a day.
She had no idea any of it was important, which meant she had no reason to shade anything, and no reason to remember afterward that she had been asked.
She kept no record, sent no message, and left no trace of any kind.