Devil, Darling, Spy by Matt Killeen

The deadliest weapon is a girl with nothing to lose – Sarah is used to spying in the champagne-fuelled parties of Nazi Berlin. But her new mission is infinitely more deadly – tracking a lethal disease across bullet-torn Africa, to uncover the monster who would use it to create fifty million corpses. Her enemies think she is a terrified little girl. But she is a warrior set to burn them all.