and she was confused by the ending so i was breaking it down for her
what i said, what i took from it, was
the first part is a young inexperienced writer (writing a novel out of real events) - her judgmental nature and slight snobbery come across on every page
the second part, she has matured technically but still has some naive ideals that underpin her work - ie. everything works out sort of OK in the end
the third part, which is narrated 1st person in the book and uses the interview ploy in the film, she admits she's aware of the conflict between reality and fiction. she tries to persuade you that the happy ending was better; but i think the actual writer (McEwan) is suggesting otherwise, when you consider the illness she has and the fact you DO find out what happened

it's the 'danger of fiction' that every novelist faces
ie. they become the arbiter of some moral situation
in Atonement, McEwan lent the problem some more urgency by making it a 'true story' where the author-character's desire to arbitrate had caused a real-life catastrophe