"... There were other Koeppens in Milwaukee County at the time, but haven't been able to connect them. ..."
I've indexed about 100 Koeppen Köppen & Koeppin names in "Milwaukee's German Newspapers; an index of death notices and related items" (1844-1950). There may be some matches to your posting (Caroline? or others). Other surnames referenced with Koeppen include: Kunz Hoppe Hopp Franke Schoeknecht Pusch Fritz Kiphutt Koester Lahl Rossow