The Diamond Eye by Kate Quinn
Wry and bookish history student Mila Pavlichenko organizes her life around her library job and her young son - but Hitler’s invasion of Russia sends her on a different path. Given a rifle and sent to join the fight, Mila must transform herself from studious girl to deadly sniper - a lethal hunter of Nazis known as Lady Death. When news of her three hundredth kill makes her a national heroine, Mila is torn from the battlefields of the eastern front and sent to America on a goodwill tour.