Margaret Guthrie was christened 11 Sep 1782 at Arbuthnott. Her parents Robert Guthrie and Jean Christie were married 5 Jul 1769 Marykirk. Both events are extracted entries from the IGI. You may already know of this :-
1841 Census of Peterhead. Light House Alexander Harp 55 Light Keeper Elizabeth " 23 Jean " 21 Helen " 20 Isabella " 15 born England Ann " 14 born England William Davidson 35 Labourer
All were born outside the County i.e. Aberdeenshire except Isabella and Ann. Alexander's wife, Margaret Guthrie would have died sometime after 1827.. I now have the dates and places of birth for Elizabeth, 1 Oct 1814 Fordoun; Jean, 28 Feb 1816 Arbroath; Helen 1 Jan 1819 Arbroath.