Did Christopher Charles Wagner die in Milwaukee in 1918? If so, the family placed death notices in Milwaukee's German language press (sometimes confused with "obituaries" which are published at the discretion of a newspaper). Whether these notices are brief or detailed depended on what the family decided.
There are a daunting 1100+ Wagner entries or references (only 25 for Ehr, 6 for Holbach) indexed in the local resource called "Milwaukee's German Newspapers; an index of death notices and related items" (1844-1950) / an ongoing, independent project created, compiled and edited by Gary R. Rebholz.
I don't see clear matches in the index for a Catherine / Katharine, but it's always good to check by death or burial date to pick up the variety of related clippings that may be published.
Good luck!