One True Thing by Anna Quindlen

Ellen's father demands her return from a fledgling journalism career to care for her terminally ill mother. Her two brothers are in college, and no one else will do. During the months that follow, Ellen turns into nurse and housekeeper, recognizes her mother as the "one true thing," and slowly becomes aware of her father's shortcomings. When the end comes, Ellen is accused of mercy killing and fights the charge. Strong language. 1994.