She rose to national prominence in September 1987 when she was arrested and charged with terrorism alongside Tony Yengeni and 12 others.
[2][3] Her mother was a founding member of the Liberal Party and of the Black Sash, and in the 1980s was president of the National Council of Women.
[1][4] Schreiner's younger sister, Barbara, also became a civil servant in the post-apartheid government and was an adviser to Minister Kader Asmal.
[1] She completed a master's in sociology at UCT in 1987, with a thesis about the political organisation of women in the Food and Canning Workers' Union.
[1] She was a doctoral student at UCT when she was arrested in 1987,[6] and she later completed a master's in security studies at the University of Pretoria.
In Cape Town in 1979, she was recruited into the underground of the African National Congress (ANC), then banned inside South Africa, and went on to join the South African Communist Party (SACP) and Umkhonto we Sizwe (MK), the ANC's armed wing.
[1] On 16 September 1987, the Security Branch raided Schreiner's flat in Marie Court in Wynberg, Cape Town.
[1] She and several other Cape Town activists were detained indefinitely, often in solitary confinement, under Section 29 of the Internal Security Act,[1][8] and Law and Order Minister Adriaan Vlok told the press that they had uncovered the entire command structure of "an ANC terrorist network", calling it "the biggest-ever breakthrough against suburban terrorism in South Africa"; he also said that Schreiner was suspected of having planted a bomb in the Cape Town International Airport in July 1986.
[1] While there, they mounted a hunger strike which received public attention, demanding improvements in detention conditions, including that they – the defendants – should not be held in racially segregated facilities.
In 2021, the ANC National Executive Committee appointed her to a committee formed to provide interim leadership to the MK Military Veterans' Association,[19] and in 2022, she and Nathi Mthethwa were appointed to assist Thandi Modise as a three-man task team evaluating the status of the ANC Women's League's leadership under Bathabile Dlamini.
[20] In February 2023, she was appointed to a five-year term as a member of the ANC's internal Integrity Commission, chaired by Frank Chikane and Sophie Williams-de Bruyn.