I need some help in tracing the life of Mary Hitchings this is what I know about her so far:

Mary Hitchings married Charles Bentick in Brighton in 1847 her father was an Edward Hitchings and by 1847 he was a pensioner. 1n 1851 they were living together in Brighton and she was born in Lewes, Sussex.
In 1852 they had their only child a son William Bentick born 9 November 1852, at 7 Margaret Street, Brighton. By 1861 Mary is living with just her 8 year old son, still in Brighton, but not with Charles although she is listed as wife rather than widow. I cannot find Mary Bentick in 1871 census but by 1881 there is a Mary Bentick aged 71 at Race Hill workhouse in Brighton.
Charles Bentick dies in 1886 with his son W. Bentick in attendance in Brighton.

Mary Bentick dies 23 December 1889 in the workhouse, her informant is Edward Sattin, Master Workhouse Brighton.
I have been to the records office in Lewes looking up parish records for Mary to trace a baptisim in one of the many Lewes churches around the 1811 expected birth time, with no luck. I have been unable to find any records about when people entered RaceHill Workhouse and for what reason, so I am now wondering what I can look up now. How do I find out more about her father Edward, and who her mother was?

Any help in pointing me in the right direction would be good. Thank you.