1881 census St George Hanover Square
Elizabeth Usher 9 years, with parents Thomas (carpenter) and Harriet
1871 census St George Hanover Square
Elizabeth Usher 2 months, with parents Thomas (carpenter) and Fanny
Baptism St George Hanover Square 17 Apr 1874
Born 19 Jan 1871
Elizabeth Sophia, daughter of Thomas and Fanny USHER
Carpenter, Elizabeth Place.
Birth rego -
USHER, ELIZABETH SOPHIA Mother - DANCE
GRO Reference: 1871 M Quarter in SAINT GEORGE HANOVER SQUARE Volume 01A Page 352
My guess is that Elizabeth often changed her middle name from Sophia to Fanny, thus taking on her mother's name.