Hi Christine,
I found one Helen Petersen buried in the Manning Cemetery but no Helena Petersen.
I also found Lena Stahl.

The information below was taken from the Iowa Genealogical Society booklet --- data was collected for the society by Ging Hudson of Manning.

Each section is marked A, B, etc and the rows described below start in the North East corner of that section going north to south and the next row going south to north.
You'll notice the Lutheran church just north of the cemetery and Center street just west of the cemetery.

Section C Row 37 north to south

Helen Petersen July 31, 1833 - November 11, 1912

The other Helen Petersen listed in the cemetery records is living.

Section C Row 39 north to south

Lena Stahl 1864 - 1938
Ferdinand H. Stahl (husband) 1856 - 1936

Ferdinand Stahl Jr. 1899 - 1928
Caroline Stahl October 23, 1891 - June 19, 1910

Other Stahls that are living in Manning are Labert & Kenneth.