In her memoirs, she claimed that her marriage with Boestamam broke down due to her disagreement with the latter's decision to pay a fine to avoid a jail sentence for publishing a book deemed seditious by government in 1947.

She eventually chose to join PKMM because she believed it was more dedicated to the struggle for Malaya's independence whereas she considered UMNO a puppet of the British.

With the banning of the PKMM, API and AWAS in 1948 prior to the declaration of the Malayan Emergency followed by the mass arrests of left leaning Malay nationalists, Shamsiah retreated to the jungles and joined the predominantly Malay 10th Regiment of the Malayan People's Liberation Army of the CPM operating from Lubok Kawah near Temerloh, Pahang.

Their stint was, however, short lived as they were arrested later that year due to the anti-communist purges in Indonesia in the aftermath of the 30 September Movement.

As they were unable to return to Malaysia (established in 1963 with the federation of Malaya, Singapore, British North Borneo, and Sarawak), they settled in the town of Xiangtan, Hunan and were assigned to work in a steel factory.

Following the terms of the 1989 peace agreement signed between the CPM and the Government of Malaysia in Haadyai, Thailand, permission was finally granted on 23 July 1994 and Shamsiah returned along with her husband, their three sons and their four grandchildren.

Upon their arrival, the family was met by Special Branch officers who took them to a resort and for about 10 days, they were debriefed and briefed on the local customs and political scenario in Malaysia.

In 1981, the defected chairman of the CPM, Musa Ahmad, claimed that Shamsiah had committed infanticide by killing her third child while in the jungle to avoid capture.

[9] She subsequently denied the allegation in her memoirs and explained that she was convinced by fellow guerillas to give the child away to local villagers to be raised upon entering an unfamiliar district.