Hello again!
I have been looking into the date discrepancy. Since my grandmother said that her mother traveled over with "Mrs. Thoendel" I am wondering if Marie Zerhau, once married in the US, then traveled back to (then)Austria, and returned on the same boat as my Great-Grandmother, Marie Sitka. There is no way that she came as early as 1881, as she would have only been 14 at the time. Also, a writing from my grandmother indicates that Joseph Nickmann left Bergstadt at age 15 (which would have been in 1882) to travel to Switzerland to learn the tailor trade.
My Grandmother lived at 3120 S. Halsted St. in Chicago, and that is where all of the postcards are written to. The 1910 Census lists the Thoendel family at 6040 S. Peoria.