Who is Deidre Peabody from Immortal in Death and what is their importance?

Deidre Peabody is Eve's assistant officer, aiming for detective. Peabody admires Eve and believes that she will progress in her career if she learns to work as Eve does. Peabody also gets personally involved with Casto, who charms her in order to stay close to Eve's investigation. He does not care for Peabody, he merely uses her.