She was first of three daughters of professor David Masson and suffrage campaigner Emily Rosaline Orme.

[4] Because of her parents' social connections, Masson met Elizabeth Barrett Browning, Thomas Carlyle, Coventry Patmore and James Barrie in her youth, and heard Charles Dickens read from Oliver Twist, among other acquaintances with notables of the nineteenth century.

[7] Masson was a close friend and professional colleague of Florence Nightingale,[8] who supported Masson's promotion to Matron and in disputes with hospital administration and medical leaders around competency of staff; Nightingale arranged for practical support and influenced decisions made.

[9] Masson was active in the women's suffrage movement with her mother and sister,[6] a policy that her father also supported, speaking out when many men remained sceptical.

[11] Masson joined the Ladies' Edinburgh Debating Society (LEDS) in 1881,[6] which hosted discussions and lectures on various feminist topics, including suffrage, marriage, and religion.