My husband has Thormaehlens in his mother's maternal side (Frauen/Schilling) of the family, but they are way back in the ancestor list. We have a "Metta" or Margareta Thormaehlen born 1772 in Herzhorn (near Suederau) who married a "Toenjes" or Hans Schilling. Metta's father was a Hinrich Thromaehlen born 1727 in Sesster/Glueckstadt (also near Suderau) who married a Margaretha Engelbrecht born 1735 in Moordieck, Kreis Steinburg. Hinrich's father was a Hans Thormaehlen who married a Margeth Glashof. Since all of our Thormaehlens came from the same area (Suederau) of Schleswig-Holstein as yours, perhaps your Thormaehlen is a descendant of one of ours. I'll look into the rest of the Thormaehlen information I have to see if any line descends to the mid-19th century. Hope the place names help you further with your Thormaehlen research.
B Friis