Showing A Caress of Twilight by Laurell K. Hamilton

She is Princess Meredith and she is heir to a throne - IF she can stay alive long enough to claim it. Unlike most of her kind, Merry is part human and all too mortal, as her cousin and arch rival knows only too well. For a deadly game is being played in the Faerie court and whoever produces an heir first wears the crown. But as she auditions her royal guard - illustrious warriors equally at home with gun and blade or spell - for the role of future king and father of her child, Merry is somewhat distracted from her career as a private investigator.

Then, in her adoptive home, in the City of Angels, people start dying in mysterious, frightening ways. What the human police don't realize is that the killer is hunting the Fey as well. It seems chaos awaits, threatening the very existence of the place known as Faerie is in grave danger and Merry finds herself facing an ancient evil that threatens the very fabric of her world. And that's just the day job...