In 2008, Anna-Elisabeth von Treuenfels-Frowein supported the campaign of the citizens' initiative “We want to learn” for the referendum against the introduction of primary schools, which campaigned against the abolition of grammar schools in their current form and against the introduction of primary schools. The initiative was supported solely by the FDP, which led to the first contact with the Free Democrats. In March 2009, she joined the Hamburg FDP and was primarily involved in education policy. She was the FDP campaign manager for the referendum and the referendum on 18 July 2010 against the school reform in Hamburg negotiated by the then black-green government under Ole von Beust and Christa Goetsch.
In the subsequent parliamentary elections in February 2011, she stood as a candidate in her constituency of Blankenese and was elected to the Hamburg Parliament in the fourth position on the FDP list. She became deputy chairwoman of the FDP parliamentary group in February 2011 and was a member of the School Committee, the Committee for Justice, Data Protection and Equality and a deputy member of the Family, Children and Youth Committee and the Science Committee in the 20th parliamentary term.[4]
In the 2015 parliamentary elections in Hamburg, she was re-elected to parliament with 2.8 per cent via her state list position 4. In the 21st parliamentary term, she continued to be a full member of the Committee for Justice, Data Protection and Equality, the School Committee and a deputy member of the Family, Children and Youth Committee and the Science Committee.[5]
After the previous parliamentary group chair Katja Suding was elected to the German Bundestag in the 2017 federal elections, von Treuenfels-Frowein was elected chair of the parliamentary group together with the previous Parliamentary Secretary Michael Kruse.[6]
At the end of September 2019, she was elected as her party's top candidate for the 2020 parliamentary elections. She prevailed with 62.4 per cent against Sat.1 editor Sonja Jacobsen. She won a constituency mandate in her constituency of Blankenese and, after the FDP failed to reach the five per cent hurdle, was the only representative of her party to re-enter Hamburg parliament. In April 2021, she ran for the second place on the FDP Hamburg list for the 2021 federal election, but was defeated by the former federal chairwoman of the Young Liberals Ria Schröder.[7]
On 11 July 2024, von Treuenfels-Frowein left the FDP and joined the CDU.[8] On 7 September 2024, she was placed second on the Hamburg CDU's state list for the 2025 parliamentary elections.[9]