She was 86.
Her death was announced on April 14 by the federal chancellery, The Associated Press reported.
The cause was not specified.
Mrs. Kopp was one of the more left-leaning members of the conservative Radical Democratic Party, known for her work on environmental issues as well as for advancing women’s causes, and polls showed her to be popular.
But the effort to elevate her to the council prompted her political enemies to stir up dirt on her husband, Hans Kopp, a lawyer.