Did Fanny Whitford marry Charles Peat in Lewisham in 1869?
If so, this would be her death? --
Frances Peat
father Nichols
mother unknown
1897, St Peters district, NSW
and would Charles Nicholas Peat, son of Charles and Frances, who died in Rockdale district in1841 be their son? And possibly Charles Peat, aged 78, who died in St Peters in 1899 would be her husband.
1871 census in Camberwell shows Fanny born c1823 and Charles born c1821, so that would fit the 1899 age at death for Charles.
Anyhow, what I'm getting at is: Australian death certificates generally show considerable detail about a person's spouse and children. If you don't have Frances's death certificate, it could be worth getting, as it might show Eliza's name, depending on what the informant knew. (Since Australian certificates are so expensive, a transcription service can be a better option: google joy murrin transcription for one that many people recommend.)