You have really been a great help. Without the info you found, I would probably be looking for another week or longer.
There is another Elizabeth Thompson in the Glengarry area (father Benjamin Thompson b. abt 1801) that is older but I plan to put a message on the Glengarry board and research her also. Since she lived in the same area as Hugh McMillan, maybe there is a remote chance that she might be the one.
Thanks again for all your help,