We never get to "meet" Eleanor, who died in a car accident the year before the events described in the book. We know that she and her sister Violet were super close—so close they ran a popular web magazine together. Violet tells Finch:
"She was smart, stubborn, moody, funny, mean when she lost her temper, sweet, protective of the people she loved. She was my best friend." (16.36)
Her character is mostly vividly sketched by her absence, which is keenly felt by Violet.