Regent

With Canada now on the Ohio River, the imperium needs allies. Aurelia, the 25-year-old niece of the Empress, leads an army through the deserted ruins of the northeast US to establish contact with the Northern Federation. An illegal side trip has her talk politics with the Archbishop of Montreal followed by a jaunt to see the tiny spaceport of Canso, Nova Scotia.  There, she falls in love with a rocketry tech before being forced to defend it and him against thirty pirates, who she kills with rifle, pistol, knife, hands, teeth.
With the Empress called first to Japan and later to Mars, Aurelia hurries home to act as Regent in her place.  But that leaves her lover arrested and the imperium teetering on the brink of a war it cannot afford.