The new Mrs. de Winter has spent most of the novel under the shadow of Rebecca. She is not used to being the mistress of a wealthy estate like Manderley, and Mrs. Danvers constantly lies, telling her that Maxim loved Rebecca and that she is nothing next to her. The young narrator's many insecurities make it easy for to believe that her husband does not love her.
After Maxim confesses to his new wife that he had a miserable marriage with Rebecca, who married him only for his status, she begins to realize that Maxim truly loves her. He tells her of Rebecca's cruelty, arrogance, and infidelity. Rebecca, knowing she is dying of terminal cancer, goaded him into killing her.
Once the new wife learns all of this in chapter 20 and realizes that Maxim really does love her, she gains new strength and confidence from this knowledge. She is galvanized by knowing that Maxim needs her help. She is determined to stand by him and do everything she can to help him cover up his crime. She comforts him by emphasizing their solidarity:
They can't prove anything. No one knows but you and I....We are the only two people in the world to know, Maxim. You and I.
The young Mrs. de Winters is a retrograde portrait of a woman who finds her identity and purpose through a man. His love affirms her worth, and she becomes determined to do anything she can to support him.