Aileen Anna Maria Douglas was the daughter of a miller, John Douglas, and his wife, Bridget Murphy. She was born in County Cavan, Ireland, probably sometime between 1861 and 1863. Little is known of her early life. She may have been trained and worked as a nurse before she arrived at the age of 17 in New Zealand, where at first she worked as a domestic servant. At Blenheim on 2 September 1880 she married Frederick Garmson, a carpenter from Australia. They were to have four children: a son and a daughter were born in Sydney in 1883 and 1884; a daughter was born in Invercargill in 1886; and another, who died in infancy, was born in Melbourne in 1887.
Aileen Garmson became active in the shearers' union in Christchurch in the mid 1890s. It is likely that she had previously been involved with the shearers' union in Australia, which had close links with its New Zealand counterpart. She later claimed to have been closely involved with the 1890 maritime strike in Australia and the Broken Hill miners' strike of 1892. In July 1893 she joined the committee of the Christchurch branch of the Amalgamated Shearers' and Labourers' Union of New Zealand. In October that year she was elected treasurer, and later became secretary until 1896. As the Christchurch delegate she attended the 1894 and 1895 conferences of the union (by then called the New Zealand Workers' Union).
Garmson first came to public notice by writing well-expressed letters to the editors of the Lyttelton Times, the Oamaru Mail and other papers on such subjects as the often squalid working conditions of shearers and domestic servants. She was also active in 1893 in the campaign against the government's selling, rather than leasing, the subdivided Cheviot estate. The shearers' union hoped to prevent the evils of 'land-jobbing and syndicating' – practices by which separate pieces of land were aggregated into large holdings – which Garmson herself had observed in Victoria.
In 1894 a violent shearers' strike in Australia led the Australian pastoralists to recruit non-union labour in New Zealand. Free passages were offered, and 150 men boarded the Hauroto at Lyttelton. Aileen Garmson booked a steerage passage on the ship as the union's delegate. She harangued the men to such effect that, by the union's account, 75 left the ship at Wellington and only 33 of the remainder went shearing after landing in Sydney. She claimed to have then taken charge of the Sydney office of the Australian Workers' Union for 10 days. On her return to Christchurch she gave an optimistic report to the union, but despite her effort the strike failed.
It is remarkable that Aileen Garmson was elected to run the shearers' union at a time when even the executives of unions representing women workers were almost wholly dominated by men. She was an articulate and forceful speaker with a command of the gritty language of shearers, while her letters to the newspapers gave her a wider audience. The Hauroto episode in particular also brought her some notoriety in the press, exemplified by a vicious cartoon published in the New Zealand Graphic in October 1894.
Aileen Garmson was also a member of the Christchurch assembly of the Knights of Labor in 1894–95. She was active on behalf of the unemployed, and supported the interests of women workers both within and outside the union. She persuaded the New Zealand Workers' Union to endorse the organisation of women into trade unions, and proposed that a women's branch of the NZWU be formed. She denounced employers for the plight of domestic servants, who worked very long hours, were denied any kind of social life and in some cases were ill-fed and poorly paid; but she was unsuccessful in her attempt to form a domestic workers' union.
In 1893 Garmson was secretary of the women's section of the Canterbury Liberal Association, and in 1895 was on the committee of the Canterbury Women's Institute, which campaigned on issues such as women's suffrage, reform of divorce laws, equal pay and the repeal of the Contagious Diseases Act 1869. She was, however, interested primarily in issues of concern to working-class women, and appears to have had little involvement with the mainstream feminist movement. She crossed swords with, among others, Jessie Mackay, prominent feminist and writer, and Grace Neill, deputy inspector of hospitals, in the latter instance over the employment of nurses.
Aileen Garmson next came to public attention in Auckland, where she appeared at a meeting of the Women's Liberal League in February 1898. A newspaper report described her as 'a slight lady, plainly dressed and wearing dark goggles', and as 'the terror of all the women in Christchurch'. She was reported to have expressed to the meeting her disillusionment with working within organisations of any kind. In December that year she was divorced from her husband, and on 5 June 1899, at Auckland, she married Charles Stephenson Wrack, a mariner. Little is known of the next period of her life. However, a reference in the weekly New Zealand Free Lance in August 1900 suggests that she continued to be involved in political activity: she was described as a 'notable figure in the Gallery just now', whose 'keen satire…has made itself felt in female political conventions on more than one occasion.'
In 1917 Aileen Wrack divorced her second husband and eight days later, on 28 February, at Auckland, married Lindsay Cooke, publican of the Queen's Ferry Hotel. He took over the licence of the Junction Hotel, Thames, in 1919. In the general election of that year Aileen Cooke contested the seat of Thames, gaining 72 votes. She was one of three women to stand in the election, the first in which women were eligible to do so. She campaigned as an Independent Liberal, advocating abolition of the Legislative Council, doubling the tax on large landed estates, and the provision of free, secular secondary education for all. She strenuously opposed prohibition. It appears that she had moderated her political views in some respects: she rejected the New Zealand Labour Party 'who represented the extremists and had never yet tried to put women on an equality with men.'
Aileen Cooke appears to have remained in Thames until about 1922, when her husband briefly took over the Whangamata Hotel. He was to die in Auckland in 1931. Aileen Cooke lived at various addresses in Auckland until her death there, at St Joseph's Home in Ponsonby, on 30 May 1951.