My Mary Robert/s married in Geelong, Victoria in October, 1855. I can't confirm exactly when she arrived in Australia but likely to have been not all that long before the marriage.
The information on her marriage registration states that her parents were John Roberts, Gardener, and Margaret Mullin, she was born in Guernsey and was 23 years old.
Having looked at the Census, I think perhaps Roberts was the "English" spelling and the surname should be Robert.
The 1841 Census has -
St Pierre Du Bois - St Peters in the Woods, District 1,
James Robert 40 J Y
Mary 35 Y
Isaac? 13 Y
Sophia 11 Y
Mary 9 Y
John 7 Y
Nancy 6 Y
Willam 2 Y
This Mary would have been born c.1832, same approximate year as my Mary, who named one of her daughters Sophia.
Does anyone have any information which might confirm the identity one way or the other.