Who is Lindsey Edgecomb from Before I Fall and what is their importance?

Lindsey Edgecombe is Sam's best friend. In many ways, Lindsey is as much to blame for Juliet Sykes' death as Sam is. Throughout the novel, Lindsey's relationship with Juliet becomes clearer. When they were growing up, Lindsey and Juliet were best friends, inseparable, much like Lindsey and Sam are today.