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It is a strong possibility. I have no info for elizabeth agnes after the 1901 census which placed her in central London near Westminster.( still single)
We are unable to locate Robert's birth registration either-we are assuming he was born in Australia.
My next thought was to look at the emigration records /shipping records for elizabeth to see if she went to America as a single or whether they married before she went ( or on the boat)
Do you have a family link?