Complex sentence: She is arguably best known to the public for having made wearing tennis socks with a suit socially unacceptable in Finland in the 1980s, a practice that up to then was a common practice for Finnish businessmen abroad.
Split into simpler sentences: She is arguably best known to the public for having made wearing tennis socks with a suit socially unacceptable in Finland in the 1980's. A practice that up to then was a common practice for Finnish businessmen abroad.