Dauntless by Thomas G. Jr. Atwood
Kacey Alexander is your typical high school graduate until she receives a chest as part of her inheritance
She looks inside and finds out that her late mother was a Sentinel, a member of an ancient order of Mages, each one dedicated to protecting humans from the forces of Darkness. She refuses to accept this until her own powers emerge, protecting and healing her body from harm.
She finds herself trapped between opposing forces, each one determined to use her to take over her city. She gathers an unlikely alliance: a gruff, older sentinel, a Dark Fey warrior, and a young woman who can control the weather.
They gather to face the mercenary Pyrus and his shadowy employer. Kacey must learn to cast aside her fears to become the warrior she was born to be and stop the men who seek to destroy her city.