PERIDOT: AVATAR by Tyree Campbell

Mars sends his avatars to wrest the magic talisman from Peridot. To lure her into a trap, those avatars include two men she’s interested in. Worse, they threaten her friends Stéphanie and Nathalie. Peridot, whose human name is Ricia Ryder, takes them to the springs in northern France, where Sequana, the Celtic goddess who empowers Peridot, has a long-dormant shrine. Peridot activates the shrine, and people come from nearby hamlets to seek cures for their infirmities.

Mars, however, is focused on the talisman. He abducts Ricia and takes her to
Mount Olympus, where there is a confrontation with Zeus regarding proprieties in battles between gods. Stéphanie, meanwhile, learns a secret about Ricia that threatens to tear apart the friendship among the three women. Peridot, who seeks to do some good in the world, may not be able to do this for much longer—not if Stéphanie, a journalist, has also become an avatar of Mars.
 
In the Peridot series:
Peridot-Three Against the Mob
Peridot - The Caesar Talisman
Peridot - Avatar
Peridot - Balance of Power