Her involvement in politics began through community action in Wicklow to prevent sewage pollution into the Irish Sea.

She grew up in the Cooley peninsula of North County Louth which is close to the plutonium reprocessing plant in Sellafield on the West coast of the UK.

She campaigned against the construction of a nuclear power plant in Carnsore Point, County Wexford in the late 1970s and for the closure of Sellafield which still operates today.

She campaigned against the use of genetically modified food stating concerns of inadequate scientific knowledge.

Ahern is founding member of the Irish Women's Environment Network and the Wicklow Greens.