Isabel Montgomery, known as "Tante Isabelle" or "Great-Aunt Isabelle," holds the title of Countess and resides at Montgomery Mansion. She offers sanctuary to Lynn Russell following the Russell family's loss of their estate, The Marble Mansion, due to financial hardship. Isabel acts protectively toward Lynn, decisively intervening when Vivian Spencer attempts to have Lynn’s horse Andrews destroyed over perceived racing inadequacies. At Lynn’s urgent plea, Isabel prevents this outcome and secures Andrews’ continued care under Lynn. Her relationship with granddaughter Sophie Montgomery proves complex; Sophie lives with Isabel yet schemes against Lynn amid inheritance-related family pressures. Despite these tensions, Isabel sustains a shared household for both young women, serving as a stabilizing presence. Isabel’s noble background aligns with her status as Countess. Through her late husband, she maintains an acquaintance with the headmaster of Saint Patrick Academy, reflecting longstanding community connections.