Hallo, Diane
The 1861 census shows:
RG9/364, folio 48 page 23
3 Archbishops Place, Lambeth, Surrey
Henry Rouse, head, mar, 32, Coachman, Suffolk - Stoke by Nayland
Hannah, wife, mar, 36, Surrey - Guildford
Louisa Sophia, daur, un, 6, Middlesex - Poplar
Sarah Ellen, daur, un, 5, Middlesex - Poplar
In 1871 there is a Sophia Rouse aged 16, born in Poplar working as a nursemaid (RG10/1323 folio 61 page 16) but no sign of a Louisa.
I checked back on the 1861 census but there was no Sophia Rouse matching the age and birthplace, so it is probable that they are the same person.
In 1881 there is Sophia L Rouse aged 26 born in London working as a nurse-domestic (RG11/0168 folio 65 page 16)
I couldn't find a Louisa or Sophia Rouse (or spelling variants) matching the age and birthplace on the 1891 census.
FreeBMD doesn't show any deaths for Sophia between 1881 and 1891, and the only possible for Louisa is:
Deaths, Dec 1886, ROSE Louisa, age 32, Rochford (Essex), vol 4a p209
Between 1881 and 1891 there are 11 marriages for Louisa Rouse and one for Sophia Rouse, so it is quite possible that one of these is your relative.
Regarding Sarah Ellen, the only possible death I found was:
Deaths Sep 1902, GUY Sarah, age 40, Whitechapel, vol 1c p160
Sorry I can't provide a full solution, but this might give you some new possibilities.
All the best
Philip