She was elected to Kingston City Council as an alderman for the Sydenham Ward in 1980, and was re-elected in 1982 and 1985. In 1985, she became the first member of council to vote in favour of a Gay Pride Day for the city. There was a strong reaction against this decision, and she reversed her position after what the Kingston Whig-Standard described as "many vicious hate calls". When Cooper first campaigned for mayor in 1988, she pledged not to proclaim a Gay Pride Day if elected. She later regretted this decision, and again supported a Gay Pride proclamation when running for re-election in 1991.
Mayor
Cooper was first elected as mayor in 1988, defeating rival candidate Joe Hawkins by over 3,000 votes. She became the first female mayor of Kingston. She was re-elected over Hawkins by a greater margin in 1991, and served as president of the Association of Municipalities of Ontario in 1991–92. As mayor, Cooper initiated a Community Economic Advisory Committee which helped establish a civic airport building and a Technology Transfer Centre for Queen's University. She was the only mayoral candidate to support a city takeover of the Kingston Public Utilities Commission in 1991, and despite her personal victory was unable to convince Kingston voters to accept the measure in a referendum. She later presided over a property tax re-assessment in 1992, which resulted in significant increases for some residents. With one year remaining in her second term, she resigned in 1993 to accept a three-year appointment as chair of the Ontario Municipal Board.
Federal politics
Cooper returned to political life in early 1997, when she campaigned for the federal Progressive Conservative nomination in the riding of Kingston and the Islands. She had not previously been a member of the party, but was persuaded to run by national leaderJean Charest. The other nomination candidates regarded her with suspicion: Doug Haunts described her as "socialist-oriented" and a possible New Democratic Party plant, while Blair MacLean referred to her as an opportunist with no roots in the party. Despite these criticisms, she won the nomination with 230 votes, against 132 for MacLean and 89 for Haunts. Although considered a star candidate, she finished a distant second against Liberal incumbent Peter Milliken in the 1997 federal election. After the election, some observers argued that voters had difficulty associating her with a right-of-centre party, and speculated that this hurt her chances of election. Alan Whitehorn, professor at Royal Military College, said "I would describe her philosophically as a left-liberal. She's certainly no neo-conservative". Milliken himself argued that Cooper "should have run as a Liberal" under ideal circumstances. Cooper remained active in the Progressive Conservative Party after her defeat, and supported Hugh Segal's bid for the leadership in 1998. In 2000, she spoke at a gravesite ceremony honouring the legacy of John A. Macdonald, Canada's first prime minister and a longtime Kingston resident. In 2002, she was appointed to the Nuclear Waste Management Organization's Advisory Council.
