A Most Improper Magick by Stephanie Burgis

At twelve years old, any proper young lady in Regency England should be sitting quietly at home, practising her embroidery and keeping her opinions to herself. But Kat Stephenson is no ordinary young lady. Kat's father may be a respectable vicar, but her late mother was a notorious witch and Kat herself is the newest target of an ancient magical Order. In the first thrilling instalment of "The Unladylike Adventures" of Kat Stephenson, there are highwaymen to foil, sinister aristocrats to defeat and true loves to capture for Kat's two older sisters. This is the first novel in a brilliant new series for girls aged 10+