The entire thing with Wikitree is - it's not just "someone else's tree". It is "our" tree, with the idea that we will have one profile for each person. As this is a wiki, it means we can all (with certain restrictions based on time-frame) edit the contributions made by others.
As such, we need to be very careful when attaching one person to another that we actually have the correct person.
The correct wife for 1808 Andrew Simpson is not someone born in America, married in America, had her child/ren in America.
Most likely the Elizabeth Bryson who married 1808 Andrew Simpson, born "about 1815 in Lanarkshire" would be Elizabeth Bryson daughter of Robert Bryson and Jean Fleming, baptised on the 8th December 1816 in Rutherglen, Lanarkshire. (As this is the only Elizabeth Bryson registered between 1810and 1820 in Lanarkshire.)
To be sure this is the correct Elizabeth Bryson, however, you would need to buy the marriage document - because that should have the names of her parents, or at least the name of her father.