[5] While living in the Christchurch suburb of Linwood, Anderson became aware of the negative social impacts of gangs and drugs which were present in the area.

[6][9] Andersen wanted a family, which she felt was incompatible with the long work hours in Parliament,[6] so in 2006, took a job with the New Zealand Police.

[11] In a 2023 interview, Andersen stated that working under Key's National Party government as a public servant was her inspiration to run for election as a Labour candidate.

[6] At the 2008 election Andersen was a campaign volunteer for her former Beehive colleague Chris Hipkins, who was the Labour candidate in the Remutaka electorate.

[1][12] She was not elected, but her loss to the long-standing incumbent, Peter Dunne of United Future, was by only 710 votes, the third lowest margin in the country.

[17][18][19] The bill made New Zealand one of the first countries in the world to provide specific paid leave for miscarriage bereavements.

[20][21] In September 2020, controversy arose over the unusual arrangements for Andersen's office space rented by the Labour Party in Hutt South.

However, a sublease arrangement, which had been in place for decades under Andersen's predecessor Trevor Mallard, meant that Parliamentary Services (using public money) were paying the Labour Party $6,000 per annum to cover the rent, but the Labour Party was only paying the landlord, the New Zealand Professional Firefighters Union (NZPFU), $1,500 a year.

[24] At the 2020 New Zealand general election, Andersen was again Labour's candidate for Hutt South,[25] and defeated National's Chris Bishop by 3,777 votes.

[30] As minister, Andersen oversaw the progress of reforms related to digital identity,[31] legal aid,[32] and public safety.

[37] During the 2023 New Zealand general election on 14 October, Andersen lost her Hutt South seat to National Party candidate Chris Bishop by a margin of 1,332 votes, [38] but was re-elected to Parliament as a list MP.

Andersen yelled at the female volunteer and her brother at a Labour Party Lower Hutt election night event on 14 October.

[44] On 5 December 2023, Andersen was granted retention of the title The Honourable, in recognition of her term as a member of the Executive Council.

[45] On 21 February 2024, Andersen attracted media attention for remarks she made about National MP and cabinet minister Mark Mitchell during a Newstalk ZB interview hosted by Mike Hosking.