Find Ancestors

Hi, I am trying to find information on Mary Eaton b. Tallaght, Ireland, c. 1830, daughter of Michael and Ann Eaton of Dublin, Mary married my great grandfather Thomas Cleary from Co. Clare. Thomas and the Eatons were living in Leeds, where he married Mary, in 1852. I have their wedding certificate and can place the Eaton's at 6 Blackwell Street, Leeds in the 1851 Census. I can place some of Mary's siblings and also Mary and Thomas Cleary and family, in the 1861 Census of Leeds. But there is nothing after that. I found a record of Thomas and the children arriving in Australia in 1869, but Mary was not with them, I think she may have died, but cannot find a record of her death. I think she died between the latter of 1861 and 1868 in Leeds. It could have possibly been in childbirth, as my great grandfathers death certificate records an extra son named James, who did not come to Australia with the other children. James would have been born and died in Leeds between the latter of 1861 and 1868.
There was a family story, that Mary came to Australia with Thomas but died shortly after and Thomas deciding there were no Irish Catholic women of that time, suitable to care for his children, went back to Leeds to get a second wife and bring her to Australia. He married my great grandmother, Elizabeth Kelly, b. 1842, Queens County, Ireland at Bradford, Yorkshire in October 1868. I have that certificate also. As I said the only record I can find of Thomas arriving in Australia in in January, 1869 on the Ship the Southern Empire, with the children. Elizabeth followed in May 1872 for some reason.
I can find no record of Mary Eaton/Heaton's death in Australia, which leads me to believe she died before she could get here. I have requested copies of a couple of English Death certificates of Mary Cleary's nee Eaton/Heaton between 1861 & 1868 but neither have been her.
If anyone can help me with this saga, I would be deeply appreciative.
Regards
Diane