"Deu" is short for Deutschland (Germany in German). Stadt Hannover means the City of Hanover, which was in the province of Hannover, state of Lower Saxony. This information is likely from the LDS site. If you have identified this as the correct individual, you should be able to have a look at the original record on microfilm to determine her parentage.
Alphonso was in Dubuque as early as the 1856 state census, so you should be able to find a marriage in the area around 1870.