Background: Bertha Maria Caroline _____ was born in Zurich, Switzerland on 1 May 1875. At some point in her childhood, she met an American couple who were on a European trip. The husband Lemuel Hayward (b. about 1826, Massachusetts) was a broker in Keene, New Hampshire. His wife was the former Martha Adams, b. about 1829 New Hampshire. Eventually, the Haywards adopted little Bertha and took her to America. Bertha married in New Hampshire in 1895 and had four daughters, all of whom are now deceased. A granddaughter now seeks to learn more about the birth family of Bertha. Family tradition suggests the adoption of Bertha occurred in Zurich on 1 May 1885.
1920 and 1930 census records disagree with that tradition, instead suggesting Bertha came to the United States or was naturalized in either 1880 or 1895. Census records do agree that Bertha was born in Switzerland and that both her parents were born in Switzerland. Oddly enough, the census further indicates that Bertha's mother tongue was English and that her parents (born in Switzerland) spoke English as mother tongue.
Two Questions: 1. Since the birth name of little Bertha is entirely unknown, is there any possibility of locating any official documents in Zurich that may refer to her adoption. 2. If so, where would one go to research those potential records?
Postscript: I am not related to the above subjects. Instead, I am posting this query on behalf of a friend of my mother. I will forward responses to my mother and she will relay them to her friend (who is not computer literate).