She was born Smith in Notting Hill, possibly in the 1870's, do you know if she married Dodge in England? It would seem likely as a single woman going to Africa at that time was rare.
There were 760 Nellie Smiths born in London in the 1870's, I am not sure which registration didtrict Notting Hill was in then I thought Bloomsbury but can find no registrations there. Using Kensigton there are a dozen possibles but only one ties with the marriage below:
Name: SMITH, Ellen Mary M
Registration district: Kensington
County: London
Year of registration: 1875
Quarter of registration: Jul-Aug-Sep
Volume no: 1A Page no: 45
There is one possible marriage:
Name: SMITH, Ellen Mary
Registration district: Kensington
County: London
Year of registration: 1888
Quarter of registration: Jul-Aug-Sep
Volume no: 1A
Page no: 396
MarriageFinder: Ellen Mary Smith married DODGE, George
Do you have any ideas about the daughter?
The first step would be the marriage certificate I think.