Barbara Parker is a student at Luna Nova Magical Academy, where she is most often seen in the company of her best friend, Hannah England, and their shared idol, Diana Cavendish. She is a girl of average stature with straight, waist-length black hair and teal eyes. Her standard uniform consists of a dark blue jacket and skirt over a white shirt and tie. As a witch in training, she possesses her own magic wand and broom.

In terms of personality, Barbara is frequently portrayed as mocking and condescending, particularly toward the protagonist Akko Kagari and her friends, whom she views as incompetent and childish due to their struggles with magic and their admiration for the performer Shiny Chariot. This behavior extends to giving her targets nicknames like "Invisible Lotte" and "Creepy Sucy". Despite this smug and antagonistic front, Barbara and Hannah both exhibit a significant fearful side, becoming visibly frightened when faced with genuine danger such as monsters, curses, or even an angry Akko. Beneath her loyalty to Diana, she can be somewhat sycophantic, often flattering Diana's prestigious family background and studious nature.

A key, more personal aspect of Barbara's character is her secret enthusiasm for the Night Fall series of gothic romance novels. She initially hides this interest because Hannah finds the books stupid, and she fears being mocked by her closest friend. This hidden fandom creates an unexpected connection with Lotte Jansson, a member of Akko's friend group who shares her love for the series.

Barbara's role in the story is primarily as a supporting antagonist and a loyal member of Diana Cavendish's inner circle. She and Hannah act as Diana's constant companions, assistants, and vocal supporters, often participating in the casual bullying of Akko to reinforce their own social standing as traditional, gifted witches from magical families. In the broom relay race, she assists Hannah in sabotaging Akko's broom by transforming it into a rickety cart.

Her key relationships evolve over the course of the narrative. Her relationship with Diana Cavendish shifts from one of simple sycophancy to genuine friendship and loyalty. When Diana is forced to leave Luna Nova, Barbara and Hannah are left devastated and later express sincere, if somewhat uneasy, gratitude to Akko for helping bring Diana back, admitting it was something they could not accomplish themselves. Her relationship with Akko and her friends also softens following these events. After Diana's return, she and Hannah largely cease their mocking and are later seen genuinely happy for Akko when she finally manages to fly. This reconciliation is most evident in her relationship with Lotte Jansson, as Barbara is eventually shown openly reading and discussing Night Fall with Lotte, no longer afraid to admit her fandom.

Regarding her magical abilities, Barbara is shown to be a reasonably skilled witch. She is proficient in flame magic, capable of creating powerful fireballs, a fact that Akko herself acknowledges. She also demonstrates the ability to perform transformation magic, as seen when she turns Akko's broom into a scooter. However, her overconfidence can be a liability, as her offensive spells proved counterproductive against the magic-absorbing Ancient Dragon, inadvertently making it stronger. In the manga adaptation, she and Hannah are also shown using magic to manipulate the trajectory of a ball during a volleyball game.