Nancy could have been an infant when William & Margaret married, or she may have been their first child. A unverified database gives a birthdate of 27 May, 1844 which would definitely place her as Margaret's child as Margaret and William married in June of 1843. She was the last of the children born in Indiana.
Nancy married Elisha Wallace, 13 Dec 1863, Davis Co, Iowa. She died sometime after 1887 when she testified on behalf of her younger siblings when they applied for back payments due for their father's disability resulting from the Civil War.
1870 Census. Bloomfield, Davis Co, Iowa
The Wallaces moved back to Indiana:
Nancy WISHARD and Elisha P. WALLACE were married on 13 December 1863 in Davis County, Iowa. Elisha P. WALLACE was born in 1835 in Virginia. He died on 22 December 1888 at the age of 53 in Bloomfield, Davis County, Iowa.
Iowa Deaths and Burials, 1850-1990; FindMyPast.com
Military memorial: Private, Company G, 2nd Regiment, Iowa Infantry, Union Army