The Girl Who Kept the Castle by Ryan Graudin

Wizard West was dead for nearly an entire day before he noticed. And it is up to Faye, the daughter of West’s groundskeeper, to inform the wizard that he is a ghost who has lost all of his magical powers. (But not before the wizard tries transforming her into a cat!) To make matters worse, the enchanted castle of Celurdur—the only home that Faye has ever known—will fall apart at the next full moon if its foundation spells can’t be renewed.

After (sort of) accepting his demise, West decides to host a competition to choose his successor. Faye finds herself fighting to keep the tournament running smoothly behind the scenes: putting out kitchen fires, feeding the compost dragon, and making sure competitors stay away from the cockatrice pen. 

But killer roosters soon become the least of her worries. A servant of the evil Shadow Queen has sabotaged the contest—set on destroying not just Celurdur but the entire kingdom of Solum. It is up to Faye to stop him, but she’ll need more than a mop. Will a maid’s magic be enough to save everything she loves from utter destruction?