Millington had a decades-long career in botany; her first notable publication was the 1871 discovery of A. pusillum. She proceeded to publish a number of articles in popular science and contributed extensively to herbaria in New York. Throughout her career, she corresponded and collaborated with Charles Peck. She is commemorated alongside the rest of her family, with statues in their hometown. She functioned as a mentor to Liberty Hyde Bailey, whom she first met in 1876, when she was already established and he an eighteen-year-old studentinterested in botany.