Bruce,
I don't know how much help I will be. I was looking at the Fisher research another Fisher cousin had done. The name Nancy was popular. I found none in his research to fit.

However, my g grandmother had a sister named Nancy. She was listed as being 9 years old on the 1870 census. They lived in the Moores Prairie Township in Jefferson County Illinois in 1870. No other names you mentioned about your Nancy fit. You can find it on Jefferson County's rootsweb site. The father would have been Lewis Davis Fisher. I don't know what happened to g-grandmother's siblings, but the fore mentioned cousin might.
If you think this fits, e-mail me directly
Kathy