See the Devil's Shadow — Terry A. Burgess

Sheila Myhra just wants to know why.
Why no one had ever prepared her for the responsibility of possessing incredible powers.
Why no one had ever told her how to use those powers to battle her renegade father and his pet Demon, Malphas.
So when a legendary lost explorer, a painted buffalo hide, a haunted antique desk, a cursed spear, a vengeful woman, earthquakes, a warrant for her arrest, and picking out wedding invitations all start vying for Sheila's attention, she seriously considers throwing in the towel.
Sheila longs for the normal life she led before she was drawn into the dark world of Demons, power-hungry humans, and her own incredible legacy. And when the Spear of Longinus the fabled Roman spear that pierced Jesus' side on the cross leads her father to a secret Christian society double-cross, Sheila's wish may come true sooner than she wants.
As Sheila and Driver's blessed day draws near, so do those that wish to see Sheila exposed and eliminated. Calling in favors from old and new friends alike, it will still take all of Sheila's power, cunning, and determination just to survive her wedding day.