I am trying to help a friend from Germany. Her great grandmother, Margarete Charlotte Lindau (or Lindow) was born in Manchester on 08.12.1908. Her father, Herman is believed to have been interned. Margarete returned to Dortmund before 1930, when our friend's grandfather (who is still living) was born. They have never known the identity of his father. When I try to look up Margarete's birth on FindMyPast and Ancestry, there appears to be no record. Is it possible, that as German citizens, they did not have to register the birth? Any suggestions of places to look for Margarete (or her father's internment details) would be welcomed.