In "The Red Convertible," Susy and the brothers' adventure with her represents a last carefree episode for Henry before he goes off to war. After the war, he is forever changed. Before the war, however, Henry and his brother, Lyman buy a car, a red convertible. They spend the summer driving around, making memories that the narrator falls back on when Henry returns traumatized by the war. 

Susy forms a key part of those memories. Lyman tells us that "We went places in that car, me and Henry. We took off driving all one whole summer." One day, they pick up Susy, a hitchhiker, who is heading to Alaska. Once they arrive in Alaska, they "never wanted to leave." Their lifestyle in Alaska is simple, and they feel connected to nature. The boys stay with Susy's family, who "fed us and put us up." Lyman remembers the brothers having fun conversations with Susy. Again, this is a carefree time for Henry and his half-brother, Lyman. This is an innocent precursor to the experiences that will soon change Henry forever.

Later in the story, Henry returns home from war and is obviously traumatized by what he has seen and done. He eventually commits suicide by jumping in the river and drowning. Lyman drives the convertible into the river, where it remains forever exclusively connected to Henry. This car that once drove them around the country symbolized their innocence and carefree youth, as did Susy. Once Henry goes to war and returns, this innocence is lost. 

In "The Red Convertible," Susy represents natural innocence and freedom. She is like a guide (angelic perhaps with her abnormally long hair) as she takes Henry and Lyman to Alaska, which Lyman says is a place they "never wanted to leave." Susy's family is welcoming, feeding them and allowing them to live there. Their place in Alaska is like a dream world. Lyman says, "You never feel like you have to sleep hard or put away the world." 

They get there in summer and because they are so close to the North Pole, the days are extremely long. Lyman also notes how quickly things grow there. This place in Alaska is full of light and life, a place where you don't even feel the need to sleep. Lyman says they would doze off and wake up like animals in nature. They were completely content and in tune with their surroundings. It is a spiritual but also natural description of this place: heavenly and Earth at its best. 

Susy is the one who took them there. In doing so, she showed them an idyllic experience of nature and life. In a way, she was giving Lyman and Henry one last innocent, sublime experience before Henry goes off to war. For Henry, Alaska must have seemed like Heaven compared to the hell he would experience in the war.