I believe that this Mary E. Sittler is my husband's g-g-grand-aunt Mary Sitler.

Mary Sitler's parents were Jacob Sitler, born in Pennsylvania about 1815 and Sidney (last name unknown), born in Pennsylvania about 1820. They moved to Shelbyville, Shelby County, Illinois before 1865 (family is on the 1865 Illinois census). It is likely they moved before 1851 as the oldest child was born in Illinois in 1851.

Mary's siblings are:
Thomas J Sitler, born Jan 1851 in Illinois
Henry Sitler, born 1855 in Illinois
Francis A Sitler, female, born 1857 in Illinois
Emma C Sitler, born Jun 1859 in Illinois
Sally Sitler, born 1861 in Illinois