Isabella's close friend Gretchen Osgood Warren was a highly accomplished woman. Her mother, Margaret Cushing Osgood, was an author, and her father, Hamilton Osgood, a doctor who worked with the renowned scientist Louis Pasteur in France. She grew up moving between Boston and cities across Europe, where she studied languages, science, art, music, and literature. In 1891 she married fellow Bostonian Fiske Warren, and the two later moved to Oxford, England, where Gretchen pursued philosophy and metaphysics. When the Warren family returned to Boston, she continued to develop her intellectual interests and published several volumes of poetry. She gave copies of her poems to Isabella as tokens of their friendship.