There it was ... sitting under my nose .. for years I looked for a link ... then you found it tentatively in 2011 and then recently .. but this confirms it .. from Trove (National Library Database)
Saturday 18 July 1896 - MARRIAGE - McDONAGH-O'CONNOR. - July 1, at St Benedict's Church Sydney, by the Rev. Father Carol, Matthew Patrick, second son of John McDonagh, Co. Sligo, Ireland, to Ellen, third daughter of Patrick O'Connor, Glenastas, Co. Limerick, Ireland.

Glenastas should read Glenastar and it is a townland not far from Ardagh ... so we know for sure we have the right O'Connor's. she is the third daughter which would fit in with the 11 children on the 1911 Census and 2 children would fit in the gap between the 1858 marriage and before Ellen the first one found .. I trolled through Famsearch today without putting any surname in and they aren't there so either the register hasn't been transcribed or it was lost...

I found sometime back this info on Connor/O'Connor web page and have tried contacting the owner but he hasn't responded.

Name: Catherine, (Katie); Parents Patrick O'Connor, Bridget Kenneally; Born 1868 Glenaster, Ardath, Co Limerick; Married Cornelius Toohy (Tuohey); left Plymouth 1868 to Sydney AU; Died 1952 Carlton, Sydney AU;sis-Bridget; m 1891 Sydney, 11 chld b 1892-1912, owned dairies in Bexley & Carlton.

It is obvious a typing error re the date she left Plymouth, as she was born in 1868, but she was married in 1891 and so I am thinking that it should read 1888. Can anyone find her on a ship in 1888. I think both Bridget and Ellen her sisters and Mathew McDonagh should be on the same ship. Thanks Julie