The Fourth Sister

A troubled teenage witch, Aviva (portrayed by Danielle Harris), seeks out the sisters and befriends Phoebe with the hopes of joining the sisters, but is an unwitting pawn of an evil sorceress-priestess, Kali (unrelated to the Hindu goddess Kali), who appears to her through a mirror and has lured Aviva into some of the darker powers of witchcraft with the hope of stealing the sisters' powers and adding the Halliwell magic to her own powers of sorcery. Aviva makes a bad initial impression out of impatience and insensitivity to the sisters' blatant hints to delay Wicca talk and loses her temper as she is being asked to leave. Egged on by Kali, Aviva manages to spend some time with a sympathetic Phoebe, but having "fought" with the older Prue, is overtly hostile to her when encountered as she builds a relationship with Phoebe and then Piper. Mistaking priorities and rushing, Aviva first injures her sheltering guardian and aunt and then injures her new friend Phoebe instead of her intended victim, Prue. Awakened by the mayhem, the sisters investigate, identify the sorceress, and counter her influence on Aviva ultimately saving her.