What is the main conflict in One True Thing by Anna Quindlen?

"One True Thing" is the story of Ellen Gulden and her family in the wake of her mother, Kate Gulden's cancer diagnosis, treatment, and death. At the opening of the story, Kate Gulden is a twenty-four-year-old editor living in New York, who seems to have it all: a great apartment, a great boyfriend, and a great job. She grew up with a very close relationship to her father, George Gulden, a college literature professor who always pushed her to excel in life. George and Ellen have always had an academic bond, speaking about literature in a way that no one else understood, which made Ellen feel superior to the rest of her family, especially her mother. Kate Gulden spent her life as a home maker, dedicating her time to handicrafts and to ensuring that her household was peaceful and nurturing. Ellen always believed that her mother did this willingly, as if she hadn't had any better options. Ellen cannot imagine that Kate would have other aspirations in life than to be considered the perfect wife and mother.