Redemption: Fall of the Machines by Kaitlyn O’Connor

As Captain Ultima Hart lay dying on the battlefield, she saw THE ARRIVAL—three celestial beings that had come to save mankind.
Forward Scout Xi, Assassin Tau, and Scout Quan were assigned to track down and destroy or capture the traitor Eml. To do so, they had to take control of the Machines, the Cyborg army that Eml had designed and built to conquer Earth. Forming an uneasy alliance with the human woman they rescued, Ultima, the four set out to destroy the traitor and his army to prevent mankind from extinction.