Who is Deborah Morgan from Darkly Dreaming Dexter and what is their importance?

Deborah is Dexter's foster sister. She aspires to be a good police officer and works with the vice squad. Deborah, however, wants to leave the vice squad and work in homocide. Over the course of the novel, Deborah suspects Dexter is a murderer, is kidnapped, discovers her foster brother's true identity, and decides that protecting him is more important than anything else.