Langley made her first public appearance in 1882 at the age of nine: in Dublin, she played the obbligato violin part in Gaetano Braga's Serenata to accompany her mother, a well-known amateur singer. In November 1893 she made her London debut at the Crystal Palace, performing Max Bruch's First Violin Concerto and a Capriccio by Niels Gade under the direction of August Manns.[6] A few days later she played Louis Spohr's Violin Concerto No. 9 at the London Symphony Concerts under the direction of George Henschel. In February 1894 she appeared with the Imperial Institute Orchestra under the direction of Alberto Randegger, playing Mendelssohn's Violin Concerto.[7]
In 1895, Langley made her first appearance in a concert by the singer Emma Albani at the Queen's Hall (accompanied by the pianist Fanny Davies). She accompanied Albani on many concert tours through England, the US, South Africa, Canada, and Newfoundland over the following years. Her other musical partners around the turn of the century included the pianist Agnes Zimmermann, the violinist Alice Elieson, the sisters Louise and Jeanne Douste de Fortis, Adelina de Lara, and Percy Grainger. In the 1900/01 season, she played in the Henry Wood Proms, and in 1905 she gave the first performance of William Bredt's New Hungarian Melodies in London.[8]
In 1906, Langley founded the Thursday Twelve O'Clock concert series at London's Aeolian Hall with Mathilde Verne.[3] She also founded the Mukle-Langley Quartet with cellist May Mukle and performed in other chamber music groups. In 1907 the Quartet included Marjorie Hayward, Sybil Maturin and Adelina Leon; the line-up changed several times in later years. In 1910 she played Frank Bridge's string quartet with Mukle and the composer; in 1916, she played Maurice Ravel's Piano Trio in A minor with Juliette Folville and Warwick Evans;[9] and in 1919, she played a piano trio by John Ireland with Roger Quilter and Cedric Sharpe.[10]
Langley was also active in the English women's movement. In 1909, she performed with the English Ladies Orchestral Society, and in 1911 she participated in the Woman Suffrage Entertainment Programme for the Census Resisters, performing a concert with Ethel Smyth.[11]