Marriage
BRADSHAW Lister James
MARSHALL Ethel Maud
1924  Reg#11173
The marriage certificate would give you her age, place of birth and the names of her parents, including her mother's maiden name.
You can purchase online and immediately download AUD$17.50
https://online.justice.vic.gov.au/bdm/index-search?action=purchaseImageThere is this birth but no way of knowing if it is your Ethel
MARSHALL Ethel Maud Dashwood
Father Malcolm  Mother Annie Frances PLUNKETT
At Flemington  1898  REg#11037
However there is this marriage and death in Victoria
BRADSHAW Ethel Maude
STEVENS Frederick Ivor
1931  Reg#2032
STEVENS Ethel Maude
Father Malcolm MARSHALL  Mother Ann Frances
1983  85 years at Warrenheip 
Marriage in NSW
http://www.bdm.nsw.gov.au/familyHistory/search.htm11862/1932      
BRADSHAW  Lister J      
MCEVOY  Doris
District Waverley 
Death
3330/1968      
BRADSHAW  Lister James
Father John Mother Alice
District Sydney  
There are three death notices for a Doris [May/Mary] 
BRADSHAW on
http://www.ryersonindex.org/ There is a facility to request a lookups of the notices.  Click onto the link on the left of the home page and follow the instructions.  Results are emailed to you.  The lookups are done by volunteers.
Death
21204/1935      
BRADSHAW  David
Father Lister J Mother Doris M
District Paddington
Births are not available online in NSW post 1908.
Australian Electoral Rolls
1936  NSW
BRADSHAW Doris  16 Bourke Street, Waverley South HD
BRADSHAW Lister James  16 Bourke Street, Waverley South  Salesman
The names of any children alive or deceased would be on the parents death certificates ie if known to the informants.
A transcription of a certificate is a cheaper option in NSW.
http://www.bdm.nsw.gov.au/familyHistory/howToSearch.htm#TranscriptionAgentCheers
Cando