Elsie BOX appears in the 1901 and 1911 censuses aged 1 and 11 years old. An Elsie BOX was registered in Oxford in Q4 1899. No mother's maiden name is provided, but this is the closest birth that fits these censuses, however an Elsie BOX also marries a John THORNE, also in Oxford, in 1920, so this was very likely a different person.
No (unmarried) Elsie BOX, born in 1899 or 1900, appears in the 1939 Register.
An Elisa A BOX married Cyril S LAPTHORNE in Birmingham in Q1 1953, but this would be quite late in life for a first marriage, although the subsequent death certificate suggests that this Elisa A BOX was older, being born in 1896. But perhaps the person reporting the death didn't know how old she was...
No deaths of an Elsie A BOX can be found in Britain, suggesting that she did marry, or perhaps emigrated (no evidence).