 Petersen served in the Faroese Parliament as a representative from the South Streymoy () district from 1990 to 2008.During her first term she was mostly engaged in transport, justice, social, and health issues, and she later sat on the Faroese Parliament's financial committee.She was especially engaged in cooperation with Iceland and Greenland, and was a member of the Faroese Parliament's delegation to the West Nordic Council (formerly the West Nordic Parliamentarian Council of Cooperation) from 1990 to 2002, serving as the council's president from 1993 to 1994 and from 1996 to 1997.