[4]: 8 She was a keen activist in the Labour Party but found her idealism shattered by the twin events of 1956: the Suez Crisis and the Soviet invasion of Hungary.
O'Brien's work identified the discovery of paternity as a precursor to such patriarchal institutions as marriage and sole male rights to offspring.
O'Brien's work theorizes birth, and although her arguments have at times been dismissed as essentialist, hers is rather an integration of necessary essentialism and social constructivism.
She wrote and spoke extensively about healthcare and health care reform in Canada, with particular attention to the role and status of nurses.
The physical labour, literally, involved in women's reproductive experiences must be accounted, both as actual material production but also, more importantly, central to a sense of connection and integration of human endeavour.
O'Brien also asserted the ownership over the means of production ought to be extended to women's rights to maintain authority and control over their children.