Tammy, Gabriel Jackson McClelland was born abt. 1826 probably in Irwin County, GA and died 8 July 1857 of typhoid fever at Camp Station during the 3rd. Seminole War. He married 17 March 1853 to Lydia AnnSmith, who was born April 22, 1836 GA, and died 15 June 1901.
Therefore, Gabriel could NOT have been the father of your Martha, and I would then assume that she was then indeed the child of Allen Douglas.
However, you would still be a descendant of Lydia Ann Smith and her parents:George W Smith, born 30 June 1802 and died 4 February 1873, and his wife Caroline O'Neal Smith born 14 October, 1813,and died 6 November, 1873. George and Caroline were married 23 August 1832 in Hamilton County, Florida.
I have to go out of town for a day or so, but I would certainly like to exchange information with you, and you may email me direct at: DonnisRae@webtv.net