One of the purposes of a monologue is to give readers an opportunity to hear what is going on inside a character’s mind. A monologue can be written to reveal a stream-of-consciousness, thus giving readers the feeling that they can hear the character’s thoughts.
On the train back to District 12, Katniss is depressed, and she demonstrates the classic symptoms of PTSD. Characteristic of the syndrome, she struggles to reconcile the realities she witnessed that assaulted her strength, her emotions, and her moral code. Katniss has a psychological need to understand the terror she experienced during the games and come to terms with it. However, at the same time, she has a need to bury the pain and ignore it, as to contemplate the terrors requires that she relive them in her mind—an idea that is threatening in itself and seems too much for her to bear. On the battlefield, Katniss was a soldier in combat; her life was constantly threatened, and she was forced to kill others, but unlike typical soldiers, she was forced to kill people she knew and loved as friends. All these traumas are fresh and real to Katniss, and quite likely, they dominate her thoughts on the train back to District 12.
By returning home, Katniss hopes to live a simple life and escape from the government, and the control, and the horror of the games. However, she faces the same dilemma many other soldiers have faced when they return to civilian life after fighting in wars. She must come to terms with what she saw and experienced—she must understand it and learn to accept—before she can put it behind her and have a more or less “normal” life where she is not constantly tortured by nightmares and flashbacks of past horrors.