Tethered By Blood by Jane Beckstead

A law against female magicians.
A girl pretending to be a boy.
What could go wrong?
It’s illegal for females to perform high magic in Faronna, and there’s an elaborate execution reserved for those foolish enough to try.
Avery is one girl foolish enough to try. For three years she has disguised herself as a boy, apprenticed to a master wizard. With a talent for lying and a hunger for learning, she’s confident that someday Faronna will recognize the value of female magicians.
After a public gaffe, Avery is thrust into a new apprenticeship with an inexperienced and bitter young master wizard. Garrick Wendyn doesn’t want an apprentice, and is eager to make Avery prove her skills while he looks for any reason to send her packing.
When an opportunist bent on revenge decides to use Avery’s secret to his advantage, it will take all her wits and magical abilities to save her own neck—and that of her reluctant master.