Who is Cecilia Lisbon from The Virgin Suicides and what is their importance?

Cecilia is thirteen-years-old. She is the youngest of the Lisbon sisters. Her character is central to the first chapter of the novel, which is mainly a chronicle of her attempts at suicide. Like all the Lisbon girls, she has blonde hair but otherwise she looks much like any other teenager of the same age. She is usually seen wearing a vintage 1920s wedding dress that does not quite fit, the same dress she is wearing when she dies.