Mercy Burns by Keri Arthur

The 2nd book in the dragon series.  Mercy is Trae's half-sister.  Trae is the sexy draman in the first book "Destiny Kills".  Mercy is a reporter and she's found evidence of someone destroying draman-filled towns in the Southwest.  As she and a friend are investigating they are run off the road and her friend killed.  She has 7 days to avenge her friend's death or her spirit will roam the earth unable to pass to the next world.  Helping her is a dangerous assassin for the dragon council, a muerte.  The sparks fly between them as they try to figure out what is going on in the dragon's culture.