First you find her, then you lose her

A distant cousin popped up on WikiTree the other day, so I connected his ancestor, Janet SINTON up to her parents, James SINTON & Margaret WILKIE.
Then looked to see if there was any research outstanding on the family that might be advanced.

Janet had a sister Mary SINTON, aged 37, still living, when father James died in 1855.
But where was she between 1818 and 1855? What happened to her?
Past investigations had found no obvious death, marriage, or census entry in Scotland, and rather too many Mary anyones, preferably born Melrose or Bowden, in the 1851 census in Scotland, let alone of an age, born Scotland, in England.

So this time I tried immigration records - and turned up a Mary SINTON emigrating to New York on the "Yazoo", arriving in July 1838.
Bit of a long shot I thought - until I noticed the family above her on the passenger list.

John & Margaret FAIRBAIRN with family - known to have ended up in Ontario by Dec 1838, dying in Blandford.

Margaret was Mary's older sister.

So the chase has shifted from after 1855, likely Scotland, to finding any evidence of Mary after 1838, likely Canada but possibly USA, and her death after 1855 somewhere.