Leighton is a common surname in Washington County, too, Gloria (i.e., Margaret's biological family--Edmunds Township is down in that area--quite a drive)!

You might inquire in advance to Washington County's courthouse (clerk, probate & deeds); & Milbridge's Hist. Society may have some info (if they resided near the Harrington area).

http://www.milbridgehistoricalsociety.org/

http://www.washingtoncountymaine.com/main.html