What is Tim O'Brien's purpose in telling Mary Anne's story?

Mary Anne illustrates the way in which war serves to transform people...... all people. She arrived in Vietnam to spend time with the man she loved..... innocent and beautiful. Within what seems like moments..... she becomes a warrior, a killer..... responding to her circumstances and taking on a persona none would ever had seen had it not been for the experience of war. Her character both parallels and exagerates what these young men have gone through.