Hi Lynne
I think your other threads have included most of this information and no one has found anything of her in Scotland, Cornwall or France. I see that in some threads you say that she was a Mary Elizabeth, b.c. 1851 in England. I'm not sure where this particular info about marrying a Sinclair and dying in Scotland came from (we do need sources) but there doesn't seem to be any evidence of her in Scotland. Do you know when she died?
Also, Reid is not necessarily a Scottish name. Have you investigated them and traced them after their arrival in the UK? There maybe some clues about your great aunt in their whereabouts.
Gadget