What poem is the movie Hilary and Jackie based on?

The movie "Hilary and Jackie" is based on the book "Hilary and Jackie: A Memoir of My Sister" by Nicholas Evans. The book is a fictionalized account of the life of cellist Jacqueline du Pré, told from the perspective of her older sister, Hilary. While the book is presented as a memoir, it's important to note that it includes fictionalized elements and has been criticized for inaccuracies and artistic license.