Zanna is a gothic sibyl who had a crush on David when she was first introduced in Icefire. She is introduced as a goth in David's college, but that changes when she lends David a book on dragons. Later on she becomes the owner of Gretel, a potion's dragon who once belonged to Gwilanna.
At first, David is slightly annoyed by her - the 'wacky gothic girl on his [uni] course' - but later he falls in love with Zanna after gaining his ex-girlfriend Sophie's consent. Zanna's father is a rich dentist and she also has an older sister named Becky. Gwilanna calls her a powerful Sibyl, but also gives her three scars on her arm in a fight-- the Mark of Oomara. Gretel chooses to be Zanna's dragon, and Gwilanna disappears. Zanna is also from the line of Gwendolen, making her Lucy's half sister. She is terrified of lightning,and her best friend is Thistle.
In Fire Star, Zanna and David go to the arctic on a college geology trip. David paid to go with the money from "Snigger and the Nutbeast", while Zanna won a contest allowing her to go. She gets into a fight with David when he is needed back at home since Gwilanna has kidnapped Lucy, and is also furious since earlier they had an encounter with two polar bears, Thoran and Ingavar, Zanna almost being abducted by them. After that she was furious at David and ended their relationship stating she almost lost David in their bear encounter,after a lecture from Bergstrom. She then attends a polar bear release as Ingavar was tranquilized and brought to the biology station. As they release him, Ingavar summons Thoran and two other bears, probably Avrel and Kailar, and abducts Zanna. David hears of this and faints dead away. Zanna does not appear again until Tootega goes home and meets her there. She is given the Inuit name "Quannilaq" which means "fallen snow" by Tootega's grandfather Tartiliqug. She was apparently left there by Ingavar freezing and was thought to be the Sea Godess Sedna by the locals. She then forces Tootega to take her to the Fire Star so she can help David. She arrives in time to see David get speared in the heart with ice, and he gives her a Valentine's Day present, an invisible dragon named G'lant a name he was given by Gadzooks the last thing Zookie will write in a long time, and tells her he loves her. She then tells four guardian polar bears to break the ice under David and cries as he is swallowed up by the sea. After she returns home and while she helps release Snigger the squirrel, she reveals she's pregnant.
In The Fire Eternal, Zanna is still overcoming the shock of David Rain, her partner, dying, 5 years previously. Overcome, still, by grief, Zanna gives G'lant to Alexa, telling her that she can't take care of him anymore. To remember his death, every Valentine's Day she writes him a letter detailing the important events in her life. She has a daughter named Alexa and a small shop in Scrubbley, called the Healing Touch, where she sells tinctures (made by Gretel) and spiritualist objects like crystals. At the end of the book, she and Alexa both see David.
In Fire World, Zanna is replaced by a 12-20 year old girl named Rosanna, nicknamed Rosa. She retains most of her character traits and is unique among the other Co:pern:icans in that she was born naturally, instead of being a construct imagineered. She helps David get past the 42nd floor of the Bushley Libriarium, where they both grow 8 'spins' (years) older due to a time skip. She also sees Mr. Charles Henry (the alternate version of Henry Bacon) dead in his study, because of the time skip.
Zanna wears a lot of gothic makeup as well as a ton of bangles on her arms. She is headstrong and stubborn, but she is also very loyal and caring, especially when it comes to Alexa. Later on in the series, when David comes back, she is angry that Alexa loves him so much--that he overrode five years of dutiful mothering, upon which he waltzes in, to his accepting and happy daughter.