Can you expand on some of the information you are giving please -
"...She married somewhere around 1850-1852 to someone named Tandy - I think in the Cabramatta area of Sydney.
Why do you believe that this marriage might have been in Cabramatta area?
At the 1853 marriage, Bertha, aged ~20, would have been recently widowed?.
Can you give all the information on the marriage certificate please?
It might be the same church as the first marriage, also any children born of the earlier marriage might be on same church baptism record.
Do you have a death certificate for Bertha King, formerly Tandy, nee Glover?
I am not seeing a NSW death for Bertha King, parents George and Amelia.
Was there a third marriage for her?
When did Stephen King die?