A review of my Scotlands People searches revealed a death certificate dated July 18, 1882 for one Elizabeth Hannigan or Harrigan (Illegitimate) married to James Hannigan , and daughter of John Gordon, Chelsea pensioner (deceased, reputedly) and Mary McConachie afterwards Howie. Elizabeth died at the Doctor's Surgery in Dufftown, Parish of Mortlach, Banff.
Therefore, I am assuming that Elizabeth Gordon was illegitimate, but she later married John Hepburn and on his death married James Hannigan. James was born in Limerick, Ireland in 1810 and was a gardener, according to the 1881 census. She is listed as being 52. They are also listed in the 1871 census, although she gives her age as 50, which is correct. I wish I could age only 2 years in 10!! There is no sign of them as a couple in the 1861 census or of Elizabeth as a widow. I also have been unable to find a marriage for the Hannigans.
I found an entry on Family Search for Mary McConnachie marrying a Alexander Huie on 12June1825 at Mortlach, Scotland, and the subsequent birth of a daughter, Isabel on 11Mar1828, also at Mortlach.