This is a dystopian near-future novel and the start of a series with at least one sequel. It's told in present tense, which isn't my favorite.
Sometime in the early 21st century, either right-wingers tried to turn back the clock, or hard-core feminists staged a coup. Either way, the Second American Civil War resulted and was won by the hard-core with the help of mech warriors. These are like Heinlein's Starship Troopers, but all women. Space and the rest of Earth seem not to exist.
Seventeen years later, men and boys have been forced from power, and from most areas by zoning commissions. They aren't wanted, but are hunted down and killed or imprisoned if they try to escape. Most of the United States is the Federal Union, though traditional society, more or less, holds out in the Outlands (Appalachia, the southwest border, possibly elsewhere).
The Federal Union is big on harmony, which means conformity, blandness and obedience. Music is bland. Salt, most spices and alcohol are banned. Most travel is banned. Girls are tracked for particular job types, early. Some boys are fed steroids and sent to fight to the death with mech warrior candidates. So overall you're typical sort of controlling despotic situation.
Our heroine is Annabelle. She lives in Knoxville, Tenn-Tucky (Tennessee and Kentucky). She has been security tracked, scheduled to become a police officer. The police and mechs have the responsibility of tracking down runaway boys.
Annabelle is 16, and she doesn't like the Federal Union and its ways. She especially hates the mech warriors for killing her father and imprisoning her birth mother. When she's caught breaking into her supervisor's office to search for her birth mother, she's forced into them, or she'll be sent to a re-socialization camp in Nashville. She is also in disfavor for skipping school and suspected of helping boys (true).
Annabelle and most boys are fitted with shock collars and tracking devices. Her adoptive mother doesn't like the situation either, though Annabelle doesn't know this for a while. She agrees to become a mech to avoid Nashville. Much of the book is about her mech training and her reaction to it, to the commandant of the mech school, and to her fellow cadets, a big, domineering one in particular.
Annabelle is also trying to protect her (adoptive) sister, who wants to join the mechs. She keeps up the internal rebellion, but is only occasionally able to do anything but not shoot. Not too bad, but definitely not a world I want to inhabit. The women are often not having a good time either.
The The Rebel Within might make a good read for a less sophisticated audience, since as teens and "young adults", whom I suspect is it's target audience. More experienced readers might find it lacking.