'A Sorceress Comes to Call' by T. Kingfisher

A dark retelling of the Brothers Grimm's Goose Girl, rife with secrets, murder, and forbidden magic. Cordelia knows her mother is unusual. Their house doesn’t have any doors between rooms, and her mother doesn't allow Cordelia to have a single friend—unless you count Falada, her mother's beautiful white horse. The only time Cordelia feels truly free is on her daily rides with him. But more than simple eccentricity sets her mother apart. Other mothers don’t force their daughters to be silent and motionless for hours, sometimes days, on end. Other mothers aren’t sorcerers. After a suspicious death in their small town, Cordelia’s mother insists they leave in the middle of the night, riding away on Falada’s sturdy back, leaving behind all Cordelia has ever known. They arrive at the remote country manor of a wealthy older man, the Squire, and his unwed sister, Hester. Cordelia’s mother intends to lure the Squire into marriage, and Cordelia knows this can only be bad news for the bumbling gentleman and his kind, intelligent sister. Hester sees the way Cordelia shrinks away from her mother, how the young girl sits eerily still at dinner every night. Hester knows that to save her brother from bewitchment and to rescue the terrified Cordelia, she will have to face down a wicked witch of the worst kind.