Outpost by Ann Aguirre
Deuce's whole world has changed. Down below, she was considered an adult. Now, topside in a town called Salvation, she's a brat in need of training in the eyes of the townsfolk. She doesn't fit in with the other girls: Deuce only knows how to fight.
To make matters worse, her Hunter partner, Fade, keeps Deuce at a distance. Her feelings for Fade haven't changed, but he seems not to want her around anymore. Confused and lonely, she starts looking for a way out.
Deuce signs up to serve in the summer pat