It's possible she was visiting relatives at the time the census came around. My great grandfather was visiting his daughter in WA state in 1930 and is listed there with them instead of in MI where he died a few months later. Carolee Isaiah named sons George W. and Jonathan, and had a daughter Mary. Records call his wife Dorcas, Leorcus, Patience and Patience Dorcas, then she's missing in the 1870 Census (although Isaiah is called Married). Someone put her Patience name in the IGI, but this may have simply been based on a single Census. I found Jonathan buried at Head of the River, and my George W. (1839-1862) was originally buried at Trinity in Millville, then reinterred at Mt. Pleasant.