I see that you have tagged a number of TROVE articles, including this one:
South Australian Advertiser, 3 May 1879
HACKETT—McGONIGLE—On the 28th of April, at West-terrace Chapel, Charles Broughton Hackett, son of Mrs. Hiram Smith, of Jerilderie Station. N.S.W., to Mary A. McGonigle, late of Wentworth.
Mary Ann HALKET's second marriage was to Hiram SMITH in Victoria in 1868 Reg. number 2003. Do you have this marriage certificate? If fully completed, it should give her age, place of birth, parents' names and maiden surname, as well as details of all children from her former marriages. You can purchase an image of an historical cert online and download immediately.
It looks like Hiram died in 1885, registered at Narrandera, NSW. Mary Ann is a bit harder but if you get his death cert to find where he is buried then she may be with him. The Griffith genealogical society might also be able to help with cemetery records. This item in relation to Hiram's will says she was 'of Whitton'.
http://trove.nla.gov.au/ndp/del/article/13645119 Debra
