Who is Brita Nilsson from Mao II and what is their importance?

Assertive, persistent photographer Brita Nilsson is brought to Bill's isolated home by Scott Martineau, presumably at Bill's request, to take pictures of him for her collection of portraits of renowned writers. What none of the inhabitants of the house realize is that Brita is herself an artist, driven at this stage of her life (after years of photographing almost every conceivable kind of human suffering) by a desire to get to the truth of what makes a writer who and what s/he is.