Vivienne is shown to have "fox-red hair", "emerald green" eyes, and is rather tall, "even sitting down". According to Thea Harman, she appears to radiate "energy", with a particularly lovely voice (likely due to her mother being a healer who utilizes song in her work). At circle meetings, Vivienne is known for wearing particularly dark robes.
Although Vivienne has something of a reputation as a darker witch, and concurs with Blaise Harman's view of human boys as nothing more than playthings, both she and Selene Lucna are deeply disturbed by the Harman girl's antics and their devastating effects; Vivienne's mild bravado is only maintained until something troublesome has occurred. Vivienne is also shown to have a more tender side in regards to fellow witches, helping encourage Thea when she attempts to go after Eric Ross (though Vivienne is under the impression Thea is only using Eric for entertainment), and kindly reassures her when Grandma Harman is taken to Vivienne's mother to be healed.
Although Vivienne and Selene are both in awe of Blaise, the latter may be closer to Vivienne, going to stay with her while Grandma Harman is healed, and taking one of her projects, an enchanted necklace, with her.
Vivienne first appears in the high school lunchroom; to Thea's dismay, both Vivienne and Selene have befriended Blaise, the three of them having a reptuation for trouble. Vivienne is eager to participate in Blaise's scheme to acquire the blood of human boys they intend to use spells on, dismissing Thea's hope that there might instead be male witches around for them to engage with instead. When Thea tries to speak to Eric, once he avoids her, Selene reassures her that she and Vivienne will help her learn how to attract the boy.
At the homecoming dance, Vivienne, again wearing black, acquires the blood of her date using a corsage pin yet, when she witnesses the arrival and state of Randy Marik, a boy Blaise had mentally and emotionally destroyed in the past, both she and Selene are frightened and "shocked".
When Grandma Harman falls ill after the spirit of Suzanne Blanchet is released and kills an innocent human teenager, Vivienne and Blaise leave school to go stay at the Morrigan household, where the Crone has been taken to be healed by Vivienne's mother. Vivienne kindly reassures Thea when she arrives, but deters her from calling, as it might interrupt the ritual. After Thea confronts Blaise about the murder in the school, Blaise and Vivienne leave.
Vivienne and Selene arrive the next day at school to witness Blaise test the finished necklace; she again kindly reassures Thea, who thanks Vivienne and her mother for their help. As with the others, she is awed by the devastating effects of Blaise's enchanted necklace, which appears limitless in its power to attract and subdue the will of human males.
Vivienne is last seen at the Circle Midnight Samhain celebration, being held at Selene's house. She witnesses Blaise being taken by members of the Inner Circle, "look[ing] sober and scared".
- Vivienne's name goes slightly against the traditional witch names; it is her surname in this instance that is taken from a deity, specifically the Irish triple-goddess known as The Morrigan. The Morrigan was a group of three goddess associated with warfare and bloodshed, although the Morrigan could also be depicted as a single goddess; those they smiled upon were guaranteed victory. Usually, these three goddesses were listed as Badb, Macha and Nemain. They are famous for being the archenemy of the hero Cu Chulainn, who rejected them when they tried to seduce him. They orchestrated his death in retaliation, causing him to violate a special curse laid on him so that he would be killed in battle.
- Vivienne's given name comes from an alternate name for a legendary witch from Arthurian tales; the witch had also been known as Nimue and Vivian. Vivienne had been the lover and student of the famous wizard, Merlin, who had fallen in love with her. However, Vivienne secretly despised him, and only agreed to be his consort to learn magic and find a way to get rid of him. She ultimately lured Merlin to a hollow tree and bespelled it, trapping the wizard there forever. She is later depicted as the legendary "Lady of the Lake", who provides King Arthur with the famous sword, Excalibur, only regaining it when Arthur is mortally wounded and taken to Avalon. The name can also mean "Life", or "lively" when derived from the Latin Vivianus, which fits with the description of her as "radiatimg energy".
- Vivienne bears the same surname as Declan Morrigan, a character only mentioned on the family tree as the husband of Corisande Harman, daughter of Roseclear Harman. This could indicate that Declan is a distant ancestor or relation of Vivienne.