Hi Michelle,
Unfortunately, it may not be possible to confirm that Helen (GALLOWAY) STOTT is the same person as Helen Lindsay GALLOWAY, daughter of John GALLOWAY & Helen NICOL
Though it is encouraging that she named a son Lindsay ...
FreeCEN records the Edinburgh street in the 1841 census as
Newport St.
I see that there are entries for the 1848 marriage in Aberdour, Fife and in Eyemouth, Berwickshire - was it Ralph or Helen who was resident in Eyemouth at the time of the marriage.
I take it that you have searched on ScotlandsPeople for the GALLOWAY family in 1851 - if their Helen were still with them, that would at least be negative proof.
A search on SP for deaths of John GALLOWAY and/or Helen (NICOL) GALLOWAY might be worth doing just in case Helen (GALLOWAY) STOTT was the informant ... Though, given that John GALLAWAY (sic) and Helen NICOL married in 1812, they may well not have survived until the time of statutory registration (which began in Scotland in 1855).
I wonder whether there might have been a newspaper death notice wherever Helen (GALLOWAY) SCOTT died - which
might mention her parents. Or a monumental inscription in the relevant cemetery? I think you said she died in Luton, Bedfordshire.
JAP