Gallaher was born in Cork in 1854, but the family soon moved to Dublin where she grew up. Her parents were Sarah Gallaher (born Russell) and John Blake Gallaher who was the editor of the Freeman's Journal for nearly thirty years. She had two brothers who were writers and associates of James Joyce. She went to Alexandra College and she was then employed there as a teacher. However she was also a writer and in 1880 her novel Katty the flash: a mould of Dublin mud was published and the same year her publishers also released A Son of Man under the same pseudonym of Sydney Starr. Katty the Flash was successful and it was republished in the New York Sun and the Temple Bar magazine. The Temple Bar attributed it to "Miss Gallaher", but the New York Sun was criticised for allowing it to be amended and published under the name of her rival May Laffan Hartley. Gallaher's letter of protest to the plagiarism and unwelcome changes to her story were published in 1883 and the New York Sun was criticised by the Weekly Irish Times. The confusion continued with a modern index still attributing Gallaher's story to Hartley. Later critics have noted the stories "urban realism" whilst representing women as significant figures who are either good or bad.
