In Walk Two Moons, why does Sal decide not to send any postcards to her father?

The answer to this question comes in Chapter 10, “Huzza, Huzza,” when the travelers stop in Madison, Wisconsin. Gram asks Sal if she wants to send postcards to anyone, and the girl says she doesn’t. “Not even to your daddy?” she asks. Again, the answer is “No.” She can’t say it out loud, but postcards remind Sal too much of her mother. When her mother made her own trip from Kentucky to Idaho, she sent postcards home to her daughter at every stop. Sal remembers getting one from Mount Rushmore in the Badlands and one from Coeur d’Alene, Idaho. Her mother had written quick but loving notes on the backs of the cards. Sal wants to keep these exchanges special, between only the two of them. Sal’s memories cause us to continue to wonder what really happened to her mother; why she headed to Idaho in the first place; and why the three family members are now following her route, months later. The answers won’t become clear until much later in the book.