Neilson met the dramatist W. S. Gilbert, who cast her in her first professional stage appearance in March 1888. She played Cynisca in a charity matinée of his play, "Pygmalion and Galatea", at the Lyceum Theatre, and later that year, in the same play, she was the lead character, Galatea, in a similar matinée at the Savoy Theatre. Gilbert suggested that the statuesque young woman concentrate her career on acting rather than singing, and he coached her on acting. Her next role was Lady Hilda in a revival of Gilbert's "Broken Hearts". Gilbert wrote the lyrics to a short song for her to sing during Act I, and she proposed that a fellow student of hers at the Royal Academy, Edward German, should set it to music. She then played Selene in a revival of Gilbert's "The Wicked World". In November 1888, she created the role of Ruth Redmayne in Rutland Barrington's production of Gilbert's "Brantinghame Hall".