What is the author's style in Up a Road Slowly by Irene Hunt?

The language of the novel is relatively formal even in the dialogue attributed to Julie, who seems more mature for her character's age at points in the story. There are lapses in the formal tone occasionally, for example, when Julie switches from calling Jonathan Eltwing simply "Jonathan," an assumption of familiarity that seems out of place for a girl speaking to an older man. In another time and place, this practice is perfectly acceptable, but Julie has been trained in decorum and manners and informalities such as this seem out of character and context for this book.