 What is not a reason for Matilda to tell the librarian what happened?
The fact that in all probability such a man did not exist disturbed Matilda not in the least. She would read them carefully and then read them again, looking for the masculine names which, through a system known only to Matilda, had an affinity to her own. The first thing the widow Penshaws did was to take Matilda's left hand in her own and examine the next-to-the-last finger. Someone in Nebraska wanted to trade match books; someone in New York needed a midwestern pen pal, but it was a woman; an elderly man interested in ornithology wanted a young chick correspondent interested in the same subject; a young, personable man wanted an editorial position because he thought he had something to offer the editorial world; and— Matilda read the next one twice. Then the widow Penshaws told Matilda that she could never hope to sneak about the house without her mother knowing about it, and that even if she were going out in response to one of those foolish ads in the magazines, she would still need a good breakfast to start with like only mother could cook. Once, she told herself: Matilda Penshaws, you are being premature about the whole thing.
 she wanted to make sure the librarian stayed away from him
 she had been asked to relay a message to his wife  she wanted to tell someone her crazy story  she wanted to make sure the librarian stayed away from him  she had made a promise to return