Searches show quite a bit of information about William Ewart Gladstone Bell. He was a Professor of Music at the Sydney Conservatorium, and his two divorces were very publicly reported in the newspapers - a search of Trove, https://trove.nla.gov.au/newspaper/ will give you that information.
Mary divorced him in Aug 1928, decree granted May 1929. One newspaper article suggests they were married on "September 10, 1904, at Wishaw, Scotland, according to the rites of the Established Church of Scotland".
I found a Scotland Census, 1881, for a Mary PW Scott in Dalziel, Lanarkshire, age 2, estimated birthyear 1879, born Lanarkshire - you can find this in FamilySearch, but it doesn't provide other family members (you would probably need a subscription to get the rest of the household).
"Scotland Census, 1881," database, FamilySearch(https://familysearch.org/ark:/61903/1:1:KM2L-RYF : 10 December 2017), Mary P W Scott, Dalziel, Lanarkshire, Scotland; from "1881 England, Scotland & Wales census," database, findmypast (http://www.findmypast.com : 2012); citing p. 22, PRO T 1, The National Archives, Kew, Surrey; FHL microfilm 203,627.
I also found a death record for Mary in 1950 in the online NSW BDM, https://familyhistory.bdm.nsw.gov.au/lifelink/familyhistory/search/result?4
You would need to request the certificate (and pay) to obtain further details, but it does provide her father's name, John.
Name BELL MARY PENNYCUIK W
Registration Number 12735/1950
Father's Given Name(s) JOHN
Hope this helps you make some progress