I have had a good look, even using de Lamartine as a surname, but still can't find a birth for her. I have found a marriage for George and Fanny in 1868, and also have found them on the 1871, 1881 and 1891 census's. As Nick says there is a Florence E Birch on the 1891 census, and on 1881 she is Loui F E Birch.