Complex sentence: She previously served in the position of deputy representative during the term 1985--1989, when she represented Gro Harlem Brundtland while the latter headed the second cabinet Brundtland, until 1987 when Knut Frydenlund died and Nybakk moved up as a regular representative.
Split into simpler sentences: She previously served in the position of deputy representative during the term 1985--1989. During this term she replaced Gro Harlem Brundtland while the latter headed the second cabinet Brundtland, until 1987 when Knut Frydenlund died and Nybakk moved up as a regular representative.