Calahasen was born in 1952 and raised in Grouard, Alberta. She attended the University of Alberta, from which she received a Bachelor of Education, and the University of Oregon, from which she received a master's degree.
Calahasen first sought election in the 1989 Alberta election, when she ran as the Progressive Conservative candidates in the riding of Lesser Slave Lake. She won a plurality of votes, capturing 47.6% and defeating her nearest rival, Liberal Denise Wahlstrom, by nearly one thousand votes. This was the closest election of her political career to date; in subsequent elections, she won shares of the votes ranging from 55.5% (in the 1993 election) to 74.2% (in the 2001 election).
At the time of her election in 1989, Calahasen was the first Métis woman elected to public office in Alberta.
Calahasen served as a backbencher in Ralph Klein's government until 1996, when Klein appointed her Minister without Portfolio responsible for Children's Services. She served in this capacity until 1999, when she was shuffled to the position of Associate Minister of Aboriginal Affairs. In 2001 she was promoted to full minister, of Aboriginal Affairs and Northern Development. Calahasen initially supported Lyle Oberg in the 2006 P.C. leadership election, but switched her endorsement to Ed Stelmach after Oberg dropped off the ballot; despite this support, she was not included in Stelmach's cabinet once he became premier in 2006.
Calahasen has sponsored a number of bills over her career in the legislature.
Despite not being a member of cabinet, in 1990, Calahasen sponsored the Metis Settlements Act, a government bill which incorporated Métis settlements as a new class of municipality. It passed with the support of the opposition, although New Democrat Bob Hawkesworth expressed concern that the settlements were not given sufficient autonomy from government. The same year, she sponsored the Nechi Community College Act, a private bill that would have established the Nechi Community College but did not reach second reading.
In 1995, Calahasen sponsored the Colin Chor Wee Chew Legal Articles Act, another private bill which didn't progress to second reading. She also sponsored the Public Health Amendment Act, designed to allow nurse practitioners to fulfill some of the functions of doctors in communities in which doctors were in short supply. The bill passed with the support of the opposition Liberals, but some members, including Terry Kirkland, Colleen Soetaert, Percy Wickman, Gary Dickson, Lance White, and Howard Sapers, argued that the bill left out too many details and left the details in the realm of legislation, inappropriately empowering bureaucrats at the expense of the legislature.
As Associate Minister of Aboriginal Affairs, Calahasen sponsored the First Nations Sacred Ceremonial Objects Repatriation Act, a 2000 government bill that allowed for the repatriation of first nations artifacts. It passed with full opposition support.