"Ellen Berent's Diary" is a fictional work that serves as a narrative device in the novel "Leave Her to Heaven" by Ben Ames Williams. The diary provides insight into the thoughts and emotions of the character Ellen Berent, a complex woman whose obsessive love leads to tragic consequences. The diary reveals Ellen's inner struggles and motivations, highlighting her intense desire for control and her fear of losing those she loves. Through her writings, readers gain a deeper understanding of her character and the psychological themes explored in the story, including jealousy and the impact of obsession.