Why is April worried about the empty mailbox?

April
was sent to live with her grandmother because her mom does not have the time or desire to raise
her while also pursuing an acting career.

When the book begins, April is
devastated and quite unhappy at having been abandoned by her mother. She writes to her mom with
some regularity and eagerly awaits some kind of response from her mother. She hopes for a
letter, a postcard, something, anything, but day after day goes by, and the mailbox is
continually empty. Her mom does not respond to the letters, and April worries about the mailbox
continuing to be empty because it is further confirmation that her mom has really left her
behind.

Fortunately, April makes great friends, and by the end of the book,
she is quite content living with her grandmother.