Margaret McCay
Baptism or Birth date = 16th November 1884.
Parish = Dungiven
Father = William McCay, Farmer
Mother = Martha Quigley
Informant = William McCay
Maybe Margaret was visiting/staying somewhere else, and Head of House didn't think they had to record her.
Thomas Robert Fulton and Margaret McCay, had another daughter, called Jane Scott Fulton. Looks like one daughter was called after the paternal grandmother and the other daughter after the maternal grandmother.
On the 1911 census , is Thomas Fulton McCay , recorded with a Wray Family on Westland Avenue, Londonderry ?