Hello MargP,
No my Catherine was not born in 1823, I still believe that the family members who researched her years ago are correct, it is mainly what happened to her family, and how she got to Australia, but I will do what you suggested and perhaps find (or try) the death certificate of my g-grandmother, but as you said that would only show what people knew about them at the time.
There is too much information on Ancestry and Genes Reunited from people researching Catherine to ignore the fact as to who her parents and siblings were, it is just that none of us can find anything after the 1841 census.
Regards,
Thelly