The Witch and the Priest by Hilda Lewis

Joan Flower is long dead when she first appears to Samuel Fleming, a priest plagued by doubts about her and her daughters' execution for witchcraft. Did he do all he could to rescue them from damnation? From beyond the grave, Joan reveals to him the spine-chilling tale of her seduction by Satan, her temptation of her own daughters to the Devil's coven, her murderous sacrifices, and her final rejection by both Heaven and Hell - yet Samuel still strives for a way to redeem her sins. Over their terrifying conversations, Samuel learns the way of the witches' sabbath and comes to the dark realisation that Joan's soul may not be the only one in need of saving.