You wouldn't understand what its like out there Fossie
A medic(Mark Fossie) invites his girlfriend(Mary Anne Bell) to join him in Vietnam, at first Mary Anne is unaware of the dangers around her and is reckless, but is curious and learns the way of the camp quickly.
As Mary Anne got deeper into the life of a soldier she became more distant, and started to look more disheveled, as her appearance no longer mattered to her. The war made her realize that life in Vietnam was rough, and it changed her personality.
When Mary Anne first arrived at the site, she had a bubbly, naive personality. Although as she experienced the war first hand, her innocence was lost to the war. She realized that it was not all fun and games. She was no longer "innocent" to tragedies, she had experienced the war first hand, and could not simply push away what she saw.