Why is the moon Isabel's "friend" in Chains by Laurie Halse Anderson?

The "friendship" of the moon in the book Chains has to do with the importance of night to the character of Isabel. Throughout most of the book, Isabel is only able to see her sister (Ruth) at night. It is also the time when Isabel is able to have many of her adventures. For example, it is by the light of the moon that Isabel is able to escape from the Locktons in order to take a book (Robinson Crusoe) from the library. More importantly, it is often at night that Isabel is able to sneak to Bridwell prison to bring Curzon and the other prisoners food and warmth. The moon is Isabel's "friend" because it lights her way when she otherwise would not be able to see. In addition, the light of the moon is dim enough that Isabel cannot easily be recognized and caught.