It turns out that Nancy Elizabeth Dungan was the daughter of Thomas Wilson Dungan and Anna Farris - this makes her the younger sister of John B. Dungan.
1860 Census in Salt River, Shelby Co., MO (listed as T. Wilson Dungan and Anna) are: John B. - 1841 Sarah F. - 1848 George H. - 1851 Charles - 1854 Nancy E. - 1857
1870 census in Salt River, Shelby Co., MO Elizabeth is listed as 12
1880 census in Salt River, Shelby Co., MO - page 444c Wilson DUNNZAN Self M Male W62VAFarmerVAIN Mary DUNNZAN Wife M Female W 32 DE Keeping House DEDE Maggie DUNNZAN Dau S Female W 10 MOAt SchoolVADE Thomas DUNNZANSonSMaleW9MOVADE William DUNNZANSonSMaleW5MOVADE Myrtle DUNNZAN Sister SFemaleW2MOVADE N ellie McCOY DauS Female W 22 MO At Home VAVA