Here's your ancestor on the 1850 Forsyth Co., GA. census:
758-1 NancyGuthrey48f100ga1802 758-2 John FGuthrey25mFarmerga1825 758-3 ElizaGuthrey23fga1827 758-4 Mary AGuthrey20fga1830 758-5 NancyGuthrey18fga1832 758-6 LucindaGuthrey13fga1837 758-7 Robert HMcCoy4mga1846
Nancy's mother is obviously Nancy too. In all probability, the father is dead and Nancy is a widow. She is also listed as the head of household in the 1840 census so the husband must have died prior to the taking of that census. The youngest Guthrey child was born in 1837 so pinpoint the father's death 1837-1839. Look for a marriage bond ca. 1824 for a Guthrey (Guthrie) marrying a Nancy and you will probably have identified your man.