Hi Hazel,
I think this is going to get confusing

I can see an entry on the IGI of,
Susan SOUTHEY
B. 21 May 1825
Chr. 17 Jun 1825 St Olave, Bermondsey, London
Father: James Southey
Mother: Maria
I also think I can see this Susan age 16, in 1841 with her mother Maria living in Battersea. She seems too old.
There is also,
Susanna SOUTHEY
Chr. 01 Mar 1835 St John the Baptist, Croydon, Surrey
Father: William Southey
Mother: Sarah
I thought this one was too young but looking further there are quite a few children born to a William and Sarah between 1818 and 1835, in Croydon and Newington, some of which state birth dates as earlier than the years they were christened.
I can't find this Susanna in the 1841 census but I can find the mother Sarah with sons William and George, then in 1851 (by which time Susanna has married) I can see this family and there is also a daur. M. A

age 28 who wasn't with them in 1841, if this is the right family maybe the sisters are hidden somewhere together in 1841

In 1861 the son William seems to be living next door to George and Susannah STEER. Sounds good

or just coincidence

In the census Susan/nah STEER changes where she was born nearly everytime

although it's all the same area,
1851 Susan age 21 b. Locks Field London
1861 Susannah age 30 b. Newington Surrey
1871 Rosa S. age 40 b. Surrey Croydon
1881 Susannah age 50 b. Croydon
1891 Susannah age 62 b. Addington Surrey
It may be worth getting the marriage cert. of Susannah & George (ref. given on different thread) to confirm who her father was.
Regards
Daisy