[6] She joined active politics as a member of the CPN (ML) affiliated student union, ANNFSU.
[5] She was central deputy chair of ANNFSU at the time she graduated from student politics in 2052 BS (1995–96).
[11] She was elected to the federal parliament under the proportional representation system,[9] nominated by the Communist Party of Nepal (Unified Marxist–Leninist) (CPN UML), and elected as deputy speaker with the support of her party CPN (UML), as well as the Communist Party of Nepal (Maoist Centre) (CPN MC) of the left alliance, defeating Pushpa Bhusal of Nepali Congress, on 15 March 2018 by a margin of 143 votes.
[5] She resigned as the deputy speaker on 20 January 2020,[14] and on 17 February 2020 was appointed as the Minister for Law, Justice and Parliamentary Affairs.
[11] Subba is said to have been inspired to pursue his own doctorate (in "the political movement of indigenous peoples") from the example of Tumbahamphe.
[15] Tumbahamphe was married to Late Ghanendra Jimi, who was once elected chairperson of Urlabari VDC representing CPN (UML).