I have an instance in my family research where an aged ancestor is listed on a ship list 1840s/1850s with family but no indication found that they arrived in Milwaukee with the family. The PERSI index helped locate an indexed source to their path - they stopped in Detroit for a couple of years before moving to Milwaukee.
Going through the most logical church burial registers in Milwaukee may be another way that may help you find Lisette Schiemann (nee Buchmann). In the Milwaukee area, those become a primary source in the days before civil reporting became more consistent (not necessarily the same as cemetery records). If you haven't done it already, narrow the search by years & most logical religion, earliest known family church and/or house address, earliest known burial location for anyone in the family group?