Catherine Ann McHaffie was born at Onehunga, Auckland, New Zealand, on 1 August 1870, the elder daughter of Ellen Leatherbarrow, a Londoner, and her husband, James McHaffie, a Scot who had come to New Zealand in the West Coast goldrush. James worked as a clerk and around 1875 the family settled in Christchurch. When her mother died in 1881, Catherine took over the household duties.
Like most Scots, James McHaffie valued education. Catherine (known as Kate or Katie) attended Christchurch Normal School where she was an able pupil. Her father could not afford the fees to send her to high school, so she accepted the school's invitation to train as a teacher. She was a pupil-teacher from 1886 to 1889 and was certificated in February 1891. From then until 1900 she taught at the Normal School, where the inspectors repeatedly acknowledged her careful preparation. She gave up paid employment permanently when she married Johannes Carl Andersen, a clerk in the Department of Lands and Survey, on 9 May 1900 at Woolston, Christchurch.
Throughout her life Andersen used her teacher training to help 'the less fortunate classes'. From 1910 she was a member of the committee that worked to establish a free kindergarten in Christchurch. She spoke publicly of 'that great peril and misery…involved in mothers having to leave young children in order to go out working for their support'.
As one of the first generation of women with above average education who had known some social independence, Andersen was eager to maintain ties with like-minded women and pursue serious intellectual discussion. Acting on an idea put forward by Blanche Baughan, Mary Colborne-Veel and Jessie Mackay (three writers resident in Christchurch), she joined the committee set up to found the Canterbury Women's Club in 1913. In the manner of similar organisations elsewhere, the club aimed to be 'a centre of culture and progress' and a place to receive 'women of distinction' who were visiting the city.
When Johannes Andersen became an assistant in the General Assembly Library in 1915, the family moved to Wellington. Ill health curtailed Kate's activities, but eventually successful surgery enabled her to resume and develop the interests that she had enjoyed in Christchurch. By 1919 she was a member of the council of the Wellington Free Kindergarten Association and helped to examine their staff trainees. She was also one of its delegates to the Wellington branch of the National Council of Women of New Zealand from 1919 to 1924. Disagreeing with the association's conduct in a debate over maternal mortality, she resigned in 1925.
Subsequently, Andersen channelled her professional expertise into the Wellington After-care Association, of which she was a foundation committee member. Officially constituted in 1928, it catered for those deemed ineducable. The organisation followed contemporary thinking in emphasising the importance of play and the provision of practical training for the young. It set up the first occupation centre in New Zealand for the intellectually handicapped. The association realised another important goal: it gave parents and guardians a break from full-time care-giving. Andersen remained on the committee until 1946.
Andersen also pursued her interest in cultural activities in Wellington. In 1923 she helped found the Wellington Lyceum Club, the organisation that was to be the major focus for her activities outside the home. As president or vice president almost continuously from 1926 to 1941, she found an outlet for her confidence as a hostess, her skill as a public speaker and her ability to chair meetings. Wartime blackout restrictions temporarily checked these pursuits. Within the Lyceum Club, Andersen's particular enthusiasm was the Penwomen's Circle, which she led from 1932 to 1940. The group fostered creative writing. The decision in 1928 to publish members' work in a magazine, the Lyceum, marked the seriousness with which they regarded their efforts.
Kate Andersen helped to advance acknowledgement of women's contribution to New Zealand literature when, in 1932, she was a foundation committee member of the New Zealand Women Writers' and Artists' Society. She was president from 1935 to 1937 and vice president from 1937 to 1939. Her husband backed her endeavours. At a time when, as one of the founder members noted, women's literary creations were dismissed as 'scribbling', Johannes Andersen, librarian at the Alexander Turnbull Library and an established writer, appraised and endorsed members' efforts. In 1936 the couple made a world trip, the chief object of which was to attend the international conference in Buenos Aires of PEN, the professional authors' association.
Andersen had links with several organisations, two of which honoured her with life membership: the Women's Social Progress Movement and the Wellington Housewives' Association. In 1935 she became a justice of the peace. Realising the importance of building an archive to record women's achievements, she instituted the New Zealand Women's Biographical Society in 1945.
In 1946 the Andersens moved to Auckland, where their sons had settled. For a time Kate attended the Auckland Lyceum Club, leading its Pan-Pacific Circle. In the mid 1950s her health began to fail and diabetes was diagnosed. She died of a cerebral haemorrhage on 15 September 1957 in Epsom. Her husband and two sons survived her.