Armstrong grew up on the Lower Springfield Road in West Belfast, and went to St Rose's Dominican College in Beechmount. She left school at fifteen.[1]
After marrying, Armstrong moved to Twinbrook suburb of Belfast in 1974 and became a community worker in 1981.[1][2] At the 1993 Northern Ireland local elections, she was elected for Sinn Féin to represent Dunmurry Cross on Lisburn City Council.[3][1]
In July 1993, Armstrong's home came under attack from loyalist paramilitaries in an attempt to kill her.[1][4][5]
At the Northern Ireland Forum election in 1996, Armstrong was placed fourth on the Sinn Féin list for West Belfast, but was elected in their best result in Northern Ireland.[6] She did not defend her council seat in 1997,[3] and did not stand for the Northern Ireland Assembly in 1998.[6]
Outside politics, Armstrong established the Colin Community Forum, Colin Community Restorative Justice, Colin Health for All and Cumann na Fuiseoige GAA. She became a Director of Lisburn Strategic Partnership and the Colin Neighbourhood Initiative, and works as a Community Safety Project Worker with the Northern Ireland Association for the Care and Resettlement of Offenders. In 2008, she was appointed as an independent member of the District Policing Partnership.