I have been searching Stephen Morse's one-step sight passenger lists and have thought about multiple passages also, but since Marie Zerhau's mother arrived, I believe in Dec. 1881, and her father was dead, there would have been no solid reason for returning after 1881.
Have you seen alternate spellings for the Sitka name? I have found a "Marie Styce" b.1866, arriving 25 May 1881 (NYC), on the ship "Westphalia". This date is appx. one week before Marie and Herman Thoendel got married in Chicago. I am still searching for Marie Zerhau on that list.
I have also found "Marie Nickmann", b. 1866, arr. 29 Oct. 1891 (NYC), on the "Westernland". Do you have the Nickmann's wedding date in 1891?
Did you recieve the photos I sent you? You can reply to that e-mail or attach files at the bottom of the post page. Thanks.