Marjory Bernice STEVENS

I am looking for infomation about Marjory Bernice Stevens born 18th March 1922 in Snowtown, South Australia - she left Australia in 1946 (after being married in Sydney on the 18th April 1946) for the UK as a war bride - my question is when did she reliquish Australian citizenship and take up British Citizenship when offered by the British Government to become a British Citizen - how do I find this infomation