Kathleen Gregory, a student at St. Clare's, possesses a deep affection for animals and dreams of becoming a veterinarian. Her compassion is evident when she rescues and diligently nurses an injured puppy back to health after it was shot. She also keeps a vivarium of snails, each individually named; while most classmates recognized only one named "Dopey," Kathleen claimed she could distinguish them all.

She becomes one of the first students to befriend the initially unpopular O'Sullivan twins, Pat and Isabel, aiding their adjustment to the school. During the first book, she faces significant tension when falsely accused of stealing money, including Isabel's, an accusation eventually resolved.

Her kindness extends to objecting to a prank placing insects in a teacher's glasses case, concerned for the creatures' well-being. Kathleen remains a steadfast presence throughout multiple terms, interacting with various students like Alison O'Sullivan, Lucy Oriell, and Margery Fenworthy.