Well after nearly 8 years I may have made a slight break through!
James and Ann's daughter Menah Esther Levett married James Dunnett. She died on 11th Jun 1931 at Love Lane Melton Suffolk. Looking at the GRO web site Administration of her estate was granted to Susan Louisa Hillier wife of Thomas (Unfortunately that means no will). I then found Susan and Thomas on the 1911 census, both were born in London. However, one of their daughters was called Mena, and when I checked her birth on the GRO site, her mother's maiden name was LEVETT!
I found Susan L Levett born 1853 and her mother Sarah, a widow, on the 1871 census in Islington St Michael London. Sarah was born 1815 in Suffolk and it looks as if she was born in Tunstall.
I then found Susan and Thomas's marriage on Ancestry in 1873 and it was one of those where it shows the actual certificate. Susan's father was JAMES LEVETT, a bricklayer, exactly the same occupation as Menah's father. So I think that Menah and Susan were half sisters. Susan was 20 when she married.
So it looks as if Menah's mother may have died giving birth to her in 1851 - I still can't find a death. Her father James then either married or just lived with Sarah and they moved to London where Susan Louisa was born. I cant find her birth either.
BUT - Menah and Susan must have known about each other and kept in touch as administration was granted a few days after her death to Susan.