Elaine Lillian Mallory was Harry's first love. Both orphans, they were adopted at age ten by Justin DuMorne, within a few months of each other. They went through puberty together and ultimately became romantically involved. However, when they were 16, Justin and Elaine worked together in an attempt to enthrall Harry and recruit him into black magic. In the ensuing duel, Harry killed Justin by burning him to death in a fire that destroyed their home. Presumably, Elaine was killed as well.
Warning: The following contains spoilers for later books. Read at your own risk.
Developments throughout the series
Elaine returns in Summer Knight, very much alive. She tells Harry that Justin had enthralled her two weeks before coming after him, and that her apparently treacherous actions were not done by choice. She managed to escape the fire but was traumatized and weakened by Justin's mind control, and by the time she learned of Harry's survival, she wasn't sure he would want to see her. She found asylum with the Summer Court, a debt she must pay off by serving as Summer's emissary in the investigation of the murder of Summer Knight Ronald Ruel. Harry tries to convince her to come clean before the White Council, but she refuses to submit to their authority.
Elaine helps Harry by arranging a meeting with the Summer and Winter Mothers. When Aurora's treachery is revealed, Elaine rigs a binding for Harry that she knows he can easily escape from, saving his life. When the war is averted, Elaine leaves, but not before advising Harry to stop feeling sorry for himself about Susan and start living again.
She makes another appearance in White Night, hired on by the Ordo Lebes to find the gray cloaked man responsible for the deaths of several of their number. In the intervening years, she took a leaf out of Harry's book, opening her own private detective office and becoming the only Wizard in the Los Angeles phone book. Wishing to remain under the White Council's radar, she deliberately hid her talent when being tested by Warden Carlos Ramirez, regional commander of the western United States.
Together, she and Harry track down the killer and save all but one of the remaining Ordo women. In the process, she is seriously injured and is therefore unable to participate in the ensuing battle at Chateau Raith. She soon recovers and returns to California, but not before deciding with Harry to build a support network for middling-talent wizards like the Ordo, using the Raiths' weregild.