During her university years, Frei was a Christian Democratic student leader within the Student Federation of the University of Chile (FECH). She actively participated in the 1957 student movement in which the youth wing of her party achieved electoral victories across most student federations nationwide. In 1958, she accompanied her father during his first presidential campaign and toured the country.[2]
After returning to Chile in 1966, she participated in the commission responsible for drafting legislation on nurseries and child care centers.
In 1967, she was appointed director of a private foundation dedicated to the promotion of child care services, which bears her name. In the 1971 municipal elections, she was elected councilor of the Municipality of Santiago, obtaining the highest national vote total among councilors.[2]
Between 1971 and 1973, Frei served as a member of the National Council of the Christian Democratic Party of Chile (DC), representing party councilors.
In 1976, she settled in Larchmont, New York, where she worked for three years in the Federal Program for Assistance to Children of Latin American Origin. Upon her return to Chile in 1979, she was elected director of the Women's Department of the Christian Democratic Party.[2]
From 1979 onward, Frei became actively involved in women's opposition movements against the military dictatorship. In 1982, she joined the National Executive Committee of the Christian Democratic Party led by Gabriel Valdés. During this period, she participated in multiple solidarity initiatives supporting victims of human rights violations and presided over commissions assisting marginalized communities, including the creation of the Family Solidarity Movement, through which she organized aid campaigns for persecuted workers and residents.[2]
In 1985, Frei was appointed national councilor of the Christian Democratic Party and chaired the National Commission of former Democratic mayors and councilors. In 1987, she organized the International Meeting on Municipal Democracy, attended by more than forty European mayors and councilors.[2]
Following the victory of the No option in the 1988 plebiscite, Frei ran for the Senate in the 1989 parliamentary elections representing the 2nd Senatorial District (Antofagasta Region). She was elected with the highest vote total, receiving 58,852 votes (28.84%). She was reelected in the 1997 parliamentary elections, again achieving the first majority with 58,492 votes (35.05%).[2]
In 2005, she sought reelection for the Senate but was defeated by Radical Party leader and former Minister of Justice José Antonio Gómez. After leaving Congress, Frei continued her public activities, including serving as director of the Women's Project of the Eduardo Frei Montalva Foundation.[2]
Between 6 May 2014 and 17 May 2018, she served as chair of the board of directors of Polla Chilena de Beneficencia. In May 2018, she was elected first vice president of the Christian Democratic Party under the leadership of Fuad Chahín.[2]
On 3 January 2020, Frei was appointed coordinator of the Christian Democratic Party’s Command for the Approval of a New Constitution and later joined the Women for Approval coordination committee in the lead-up to the national plebiscite held on 25 October 2020. On 19 May 2021, she assumed the position of interim president of the Christian Democratic Party, a role confirmed by the party’s Supreme Tribunal until 2022.[2]
In 2023, Frei ran as a candidate for the Constitutional Council representing the Christian Democratic Party on the Todo por Chile list in the Metropolitan Region. She was not elected, obtaining 2.74% of the vote.[2]
