She is of medium-build, often wears a tent-like dress (which gives her a dumpy appearance), and has a shock of flyaway grey hair, a wrinkled smiling face, and the bright blue eyes of a White Witch.
Zelda is a White Witch and therefore has considerable knowledge of White Magyk as well as Magyk in general. Throughout the books she has also shown a penchance for Potion making by either making them or maintaining them.
She is sister to Theo and Benjamin Heap and Aunt to Silas although everybody refers to her as Aunt Zelda regardless of their relationship with her. She was the Keeper after completing her apprenticeship to her late predecessor Betty Crackle. The role of Keeper requires them to maintain and regularly visit the Hotep-Ra's Dragon boat who lives under Draggen island, and to escort Queen's and Princesses from the Queen's Way (the exit to which is inside of her cupboard labelled Unstable Potion And Partikular Poison's) to the Dragon Boat during their traditional visit on MidSummer's Day. On stormy nights in the Marram Marshes, Zelda keeps a lookout for any Storm Petrels which might be blown away to the marshes and hopes to meet her brother again one day. There was an instance when a Storm Petrel came to sit on Zelda's roof one stormy night and it wasn't not clear whether it was Theo Heap, although he sat on the roof and said she had always had a talent for seeing the truth in the pond to himself.
She played host to Silas, Jenna, Septimus, Nicko, Marcia and Maxie whilst Jenna was being hunted by the Hunter. She taught them how to create Shield Bugs and altered the Hunter's memory so that he believed he was a clown, in order to stop him from pursuing Jenna. She also captured Merrin Meredith who at the time thought himself to be Septimus Heap, and after being shown in the pond that he was not actually Septimus he escaped only to be Consumed by DomDaniel. Later Zelda Revived Merrin, receiving little gratitude. She tried to tell the Sheild Bugs to act as a temporary guardian until once again, Merrin escaped so he could become apprentice to Darke Wizard Simon Heap.
She played host to Wolf Boy and treated him as a son. She spent her days teaching him in the ways of White Magyk and preparing him to be her apprentice so that he may succeed her as the first male Keeper.
Zelda is sister to Theo Heap and Benjamin Heap. Her brother Benjamin married Jenna Crackle and had six son's. Her nephews are; Alfred Heap, Hengist Heap, Ernold Heap, Edmond Heap, Silas Heap and Garth Heap and she has one neice Lois Heap as well as another neice in-law (Sarah Heap).
She is the Great Aunt of Silas' seven children;Sam Heap, Nicko Heap, Simon Heap, Jo-Jo Heap, Erik Heap, Edd Heap, and Septimus Heap and adoptive grandfather to Jenna Heap. She has a brother in-law is (Titus Willow) and sister in-law (Thomasine Tremaine).
She was aprentice to Betty Crackle, a mentor to Wolf Boy and she also acted as a temporary guardian to Merrin Meredith.
She does not always like Marcia as she and her disagree on what constitutes as an acceptable use of Magyk.