How is the theme of guilt explored throughout Ian McEwan's 'Atonement'?

Guilt is a very prevalent theme running throughout Atonement, primarily centered around the central protagonist to the novel, Bryony. Towards the end of the novel the reader learns that Bryony is the author of the whole work, and wrote the entire text as a way to try and assuage her guilt for her own crime she committed as a girl- that of false testimony. Through adapting the histories of her sister and her lover Robbie Turner, Briony is able to give them the aspirational happy ending that a novelist is able to provide even though she took that possibility away from them in real life a long time ago. Briony argues that ending her novel with her sister and Robbie's eventual marriage and happy life together, instead of the cruel reality that they both died in wartime, means she is able to give them one final act of mercy and kindness. In fact Briony's view of herself as criminal who has done wrong to others is explicit: 'Her sister's confirmation of her crime was terrible to hear' (318). Writing a book is a long and arduous process, and it takes Briony the majority of her lifetime to complete the work, showing the way she is keen to punish herself and suffer as a kind of penance for what she did.
Additionally, instead of going to college and studying English as she always aspired to do, Briony decides to become a nurse and help soldiers injured in the war instead. It's obviously a job she strongly dislikes, but her sense of painful duty to help others can obviously be linked to the guilt she still feels over wronging Robbie as a child.