Sooo... if she was born about 1818, and came to NSW as a teenager while her "uncle" was Governor ( he was Governor until 1837 ? ), and he went back to Ireland, when she was about 19, then if she was going to stay .... she would have been married off to someone fairly quickly in those days. She would not have been hanging around single for another ten years or more.
Perhaps you should look at Bourke and Wills too.
Well here is something a bit interesting: from the online "australian dictionary of biography", which has quite a long entry about Richard Bourke:
"Bourke's eldest son, John, was an invalid. His younger son, Richard (1812-1904), came to New South Wales as private secretary to his father from 1831 to 1834; he returned to England to study law, was called to the Bar and practised as a barrister in Dublin. He became an assistant commissioner for the Poor Law in Ireland in 1847 and was deputy-lieutenant for Limerick. Bourke's eldest daughter, Mary Jane, married Dudley Perceval, clerk of the council at the Cape of Good Hope and later an official in the British Treasury. His second daughter, Anne (1806-1884), married Edward Deas Thomson; his youngest daughter, Frances, married Rev. John Jebb."
Now unlike most Governors, who went back to Britain and promptly died, Bourke lived in Ireland for almost 20 years after he left Sydney.
Now Edward Deas Thomson was a bigshot in the NSW Government for many many years - decades. Long after Bourke had left.
So whether your Margaret came out in the 1830's, or quite a lot later, she would have had very well placed family connections in Sydney - her cousin Anne and Anne's husband Edward Deas Thomson.