Sister Witches by Felicia Jedlicka
These nuns are doing God’s work in a less traditional way. Following the death of her father, Hennie goes off the rails. An attempted murder leads her into a life of poverty, chastity, and obedience. At least, that's what she appears to be doing. Hennie may be wearing a black veil, but her loyalties to God start with the women of her coven. She and her fellow sisters aren't just teaching bible school. They are ridding the world of evil, one exorcism at a time. If prayers are ineffective, the members of this convent will cast spells instead. Hennie's natural inclination to magic makes her an asset to the coven, but when the devil takes notice, the witches will need more than hexes to ward him off.