The Grimm Legacy by Polly Shulman

Elizabeth has a new job at an unusual library— a lending library of objects, not books. In a secret room in the basement lies the Grimm Collection. That's where the librarians lock away powerful items straight out of the Brothers Grimm fairy tales: seven-league boots, a table that produces a feast at the blink of an eye, Snow White's stepmother's sinister mirror that talks in riddles. When the magical objects start to disappear, Elizabeth embarks on a dangerous quest to catch the thief before she can be accused of the crime—or captured by the thief.