She was born on 30 March 1843 in Rome, Italy, the daughter of Vicar Canon Thomas of All Hallows Barking by the Tower.
[3] Thomas married the businessman, writer, and music collector Julian Marshall on 7 October 1864 and had three daughters.
[4] Her most successful composition, with a libretto by her sister Bertha, was the operetta Prince Sprite for treble voices, written in 1891 while she was Head of Music at Dulwich School and published by Novello.
[7] The orchestra was substantial enough to perform a Brahms symphony under her direction and the Saint-Saëns violin concerto with Mischa Elman as the soloist.
[11] Selected works include: Under the name Mrs Julian Marshall she published a biography of Handel in Hueffer's Great Musicians series in 1883, and Life and Letters of Mary Wollstonecraft Shelley in 1889.