Why does anne cling to her ideals despite the horrific world around her

Well, I would say that Anne clings to her ideals because of the horrific world around her. Even though she is surrounded by grief and tragedy, and fear of dying at any moment, she doesn't give in to that fear, and tries to live her life according to her own ideals, regardless of whether she is going to die tomorrow, or in ten years. 

The answer is 2) to show the depth of the colonists’ commitment to independence

The details that best show evidence of tribal traditions are, "never in the history of his people had a man married a woman who spoke a different tongue” and "it has never been heard," was the verdict of an old man speaking a few weeks later.