Hunter by Addison Carmichael

Anthropologist Dr. Scarlet Lupis sets out to prove that many of the ancient myths of humanlike creatures are in fact true and returns to Washington State where she spotted one 15 years ago.
After a failed mission hunting Arcans, werewolf Adam Bryant is pulled from active duty in their Pack military in order to get his head back in the game. Knowing the real issue, however, Adam returns to the place of his worst failure, determined to solve a dangerous problem that has plagued him for over a decade.
But uncovering old ghosts proves lethal for both of them when they cross the same monsters that have haunted both their lives. When Scarlet is deathly wounded her only hope for survival is Adam’s own healing Wolf blood. Now she exhibits signs that she is turning into a werewolf herself. Impossible, since she is human, all human.
And one thing all were-kind know for a solid fact—a Wolf can’t create a human shifter.