Most of her life, d'Hardelot was engaged in teaching singing and diction at her home in London and many of her pupils attained success. In 1896, she toured the United States with Calvé. Her first real success as a composer was won with "Because", though her song "Sans Toi" had previously been favorably received. Among her other successes were "I Know a Lovely Garden", "I Think", "I Hid My Love", "Dawn" and "A Bunch of Violets".
She was singularly successful as a writer of songs, in which she combined French delicacy with English solidity. Few women composers became more popular in the early 20th century than did d'Hardelot, and her success was won on merit alone. In spite of the help of many friends, it was some time before she achieved this success.