You may have lucked out if Nancy was still living with her parents in 1880. Do you have access to the multi CD set for the 1880 census? It contains an EVERYNAME index, which means you can search for a wife, child, or anyone living in the household. If you don't have access to the set, there are people ln this forum who have their own set and will do lookups. Post a query that will catch their eye "Need 1880 census lookup." And, they can search for Nancy when she would be about 14 years old. Knowing when and where she was born will also help narrow down that 1880 search.
Since you know when and where she died, you can obtain a copy of her death certificate, which should show the names of her parents, including her mother's maiden name. Accuracy only as good as the knowledge of the informant. Do you know her Soc Sec number? She filled out her own application for Soc Sec card, and that also should show the names of her parents. The SSDI (Soc Sec Dth Idx) computerized index begins with deaths occurring about 1963, so she won't show up on there, but that doesn't mean she didn't have a Soc Sec number.
Happy Hunting (^_^)