Who is Darby Shaw from The Pelican Brief and what is their importance?

Darby Shaw is a 24-year-old third-year law student at Tulane University, Shaw is Professor Thomas Callahan's current lover and star pupil. She wears baggy clothes that male students suspect cover a fabulous body. She has dark red, shoulder-length hair, and long legs: a perfect cheerleader look. A native of Denver, she graduates college magna cum laude in biology, is second in her class at Tulane, and is looking to be number one. She recites facts on virtually any case, and hopes after passing the bar to sue chemical companies for trashing the environment.