Well I don't think there is any way that Gotthilf and Wilhelmina could be Christine's parents 1) Gotthilf was born 1854 and Wilhelmina in 1856, 2) both immigrated (separately in 1880) and didn't marry till 1883 in Appleton, WI
You say "they" have Gottfried and Wilhelmina as her father and mother, who are THEY? Do you have her marriage license from Cedarburg? I found G & W's and from that I found her parents, perhaps you can find the same information on Christine and also her daughter Augusta.... Where do you live? You might want to check if there is a board for Ozaukee/Washington Co if you are not close enough to go to county records to see the records or maybe from RAK could check that information. There could well be a connection as I know one or both (Gotthilf and Wilhelmina) had siblings in Appleton that would not learn English and my grandmother and her siblings learned some German to communicate with this Aunt. I have not researched much beyond direct lines and have looked in census but not found any Gustmann or variations living in Appleton and have also tried Wagner & Wegner w/o any success beyond the siblings of grandmother and parents.....