The Watermight Thief by Jordan Rivet

Tamri is a scrappy magic thief who’s trying to get her grandmother out of the brutal canal city of Pendark. But when a quick score involving a dragon goes wrong, she’s shipped off to a distant mountaintop kingdom where the legendary Fire Queen is starting a school for magic wielders.

Tamri’s not just going there to learn. The King of Pendark suspects the Fire Queen is up to something more dangerous than training young wielders, and he orders Tamri to find out the truth. If she fails, neither she nor her grandmother will survive the school year.