Kate Challis Excelsa Hooper was born at Devonport, Auckland, on 25 June 1894 to Sophia Frances Hould and her husband, Richard Henry Hooper, a farmer who later became a journalist. As a girl Challis lived in Wellington with her parents and her mother persuaded her to became a nurse specialising in the care of children. She trained as a Karitane nurse in Dunedin from 1915, then as a midwife in the Batchelor Maternity Hospital, Dunedin (where she gained first place in the national examination in 1918), and as a general nurse in Wellington Hospital around 1921. In 1924 she became a member of the central office staff in Dunedin as assistant to Anne Pattrick, the director of Plunket nursing. Hooper worked closely with Truby King, founder of the Plunket movement, and when she left in 1932 King sincerely regretted her departure and strongly praised her work.
After a period as assistant matron of the Karitane Hospital in Wanganui in 1932, Challis Hooper was appointed charge sister of Wellington Plunket nursing in 1933, a position she held for four years. In 1937 she made a career change when she was appointed matron of the Wellington Clinic and Training School for Dental Nurses in Wellington, the first person without dental qualifications to hold that post. She was considered to be sympathetic, tactful, resourceful and decisive. During her time as matron, plans were made for a new training school for dental nurses and a new hostel. She introduced important changes into the curriculum of student dental nurses. Her Karitane training had encouraged her interest in children and she strongly believed that there should be close co-operation among all organisations dealing with children. To this end she encouraged contacts between dental nurses, kindergartens and Plunket.
Challis Hooper showed an active interest in the concerns of the New Zealand Trained Nurses' Association. She was a council member of the Otago branch and a delegate of the Association to the International Council of Nurses in Brussels in 1933. She was later convener of the Dominion Public Health Committee, a member of the Wellington Public Health Committee, and a council member of the Wellington branch of the New Zealand Registered Nurses' Association. In 1937 she became a member of the editorial committee of Kai Tiaki, the New Zealand nursing journal.
Competent, professional and forthright, Challis Hooper had many interests, including the YWCA, in which she was a member of the public affairs committee from 1956 to 1960. Her most outstanding contribution, however, was her work for the New Zealand Federation of Business and Professional Women's Clubs (NZFBPW). She joined in 1942 and in 1951 represented the New Zealand clubs at the International Federation board meeting at The Hague and at the London Congress. From 1952 to 1956 she was a very influential president: a new constitution was established which drew New Zealand clubs more effectively into the work of the federation. Better housing for women, the inclusion of women in the Apprentices Act 1948, and equality for women in jury service were other objectives of the NZFBPW at this time. The federation strenuously campaigned for equal pay for women in alliance with the New Zealand Public Service Association. In 1957 the Council for Equal Pay and Opportunity was established, with Challis Hooper as president. Partly as a result of its work, the Government Service Equal Pay Act was passed in 1960.
From 1954 to 1956 Challis Hooper was a member of the New Zealand National Commission for UNESCO, and from 1956 to 1959 was vice president of the International Federation of Business and Professional Women and chair of its UNESCO sub-committee. She led the New Zealand delegation to a conference of the International Federation in Sydney in 1955.
In 1964 Hooper was involved in organising an influential seminar at Victoria University of Wellington on the contribution of women in a changing society. This seminar, which was a joint initiative of the Wellington BPW Club and the Wellington branch of the New Zealand Federation of University Women, led to the formation of the Joint Committee on Women and Employment, on which Hooper was a founding member from 1964 to 1968.
Challis Hooper's long years of working for greater equality for women were recognised when she was appointed an OBE in 1969. She died in the Woburn Presbyterian Home, Lower Hutt, on 29 November 1982. She had never married.