Who is Macia Bonham from Johnny Got His Gun and what is their importance?

Macia Bonham is the protagonist's mother. Macia, is a fine pianist and singer, and plays for Bill Bonham over the party-line telephones during their courtship. Everyone along Cole Creek Valley listens in and submits requests. Macia also sings in the kitchen of their Shale City, Colorado home, the same wordless tune absently, repeatedly, as she works at the coal-burning stove, laying up supplies for the winter. Every Christmas she reads "The Night Before Christmas" and the nativity story from the Bible to the family.