Lodestone: Witch-Hunt by Wendy Scott

An anti-witchcraft regime is poised on Karthalon’s borders threatening genocide, unless Sabrina, a newly fledged healer, can destroy the Lodestone and restore magic.
Sabrina struggles to accept this suicide mission and is distracted by her inappropriate affection for Micah, a prospect monk.
With invasion imminent, Sabrina embarks on her quest armed only with a sliver of the Lodestone and an ancient diary, but how can one girl prevail against an army?