Robertson, New Zealand
As you may recall, the Robertson's who went to New Zealand from New Brunswick were of peripheral interest to me, and were traced no further by myself. I would assume that there was a 1901 census of New Zealand, and this may be a place for you to look. Assuming Margaret was there at the time, this should also give you her parents and their places of origin; allowing you to focus your search.
The 1901 census of New Brunswick seems to contain no Margaret Robertson who can be identified as the same you seek. Nor does the Provincial Archives of New Brunswick indicate a Margaret Roberston b. 5DEC1900. This neither means that she was not b. there, nor that her parents were not from there; but that there is no immediate indication of a connection.
If you should establish a connection to New Brunswick, let me know and I will see if something is useful.