Charlotte is Mary Smith's great-aunt and adoptive grandmother, serving as the kindly mistress of the rural English estate called Red Manor. She provides Mary with a stable home after the girl's arrival, offering guardianship and emotional support during her adjustment period. Initially portrayed as a benevolent yet peripheral guardian in Mary's daily life, Charlotte's past reveals she was once a student at Endor College. There, her exceptional magical aptitude and distinctive red hair—later inherited by Mary—set her apart. During her studies, she discovered rare "fly-by-night" flowers on campus, inadvertently triggering an obsessive pursuit of transformation magic by college leaders Madam Mumblechook and Doctor Dee. Witnessing catastrophic failures and ethical horrors in their experiments on humans and animals, Charlotte rebelled. She escaped Endor College, taking the precious fly-by-night seeds to prevent further misuse.

Following her escape, Charlotte abandoned magic completely and retreated to an isolated, sentient cottage on a small island, living an ordinary life severed from her magical past. This cottage later holds her preserved research notes, spellbooks, and a magical communication mirror. When Mary becomes entangled in Endor College's renewed experiments, Charlotte uses the enchanted mirror to establish contact. Through visions, she discloses her history as a former witch and the original theft of the fly-by-night seeds, contextualizing Mary's danger. She explicitly warns Mary about magic's corrupting nature and urges her to use remaining fly-by-night bulbs solely for a safe return home. Despite this plea for caution, Charlotte implicitly supports Mary’s resolve to rescue Peter, revealing her underlying protective nature.

Her character arc culminates in the revelation that her life choices—rejecting magic, safeguarding the flower's secret, and providing sanctuary—were driven by a desire to shield future generations from Endor's corruption. This establishes her foundational role in the conflict against the college's misuse of power.