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: