The parish records of Salem Evangelical Church, Pawnee Co., NE, give this information:
Louisa Sophia Voelz, born Priewe, wife of Mr Hermann Voelz, born 29 January 1818 in Gumtow, Kingdom Prussia, died on 29 April 1879, buried on 2 May 1879 at the local parish cemetery. Her wisdom brought her life on the same date to 61 years 3 months. Burial text, John 16:20.
This seems more likely to be the correct information. At least the calculations are more accurate than the tombstone.