Trained as a nurse in London, she began a career as a historian after noticing no history about Ayrshire whitework embroidery in books following an exhibition at the Signet Library which she visited.
Swain's research on the subject resulted in the publication of several books, she held two exhibitions, and wrote about embroidery, household textiles and tapestries in museum journals, magazines and newspapers.
A pencil portrait of Swain was made by Elizabeth Blackadder and a collection of papers and objects related to her career are stored at National Museums Scotland.
[4] In 1986, Scottish Embroidery, Medieval to Modern, was published,[2] followed by a contribution to Upholstery in Britain and America from the 17th Century to World War I the following year.
[4] The final book came after a suggestion from Glasgow School of Art embroider Kathleen Whyte and it brought all of Swain's interests in embroidery.
[3] Swain contributed to a large number of museum journals, magazines and newspapers in the United Kingdom and the United States on embroidery, household textiles and tapestries,[1][3] such as Antiques, The Connoisseur, Country Life, The Burlington Magazine, Bulletin for the Costume Society of Scotland, Bulletin of the Wadsworth Atheneum, Costume, Conservation of Furnishing Textiles, Embroidery, Furniture History, Journal of the Society of Friends of Dunblane Cathedral, Heritage Scotland, League News of St. Bartholomew's Hospital, Scotland's Magazine, The Scotsman, Scottish Home and Country, Scottish Society for Art History Journal, The Bulletin of the Needle and Bobbin Club, Pillans & Wilson and George Harrison & Co., The Daily Telegraph, The Guardian, The Times, Textile History and Waffen und Kostumkunde.
[2] Swain lectured and spoke to audiences in the United Kingdom and overseas and regularly attended conferences of the Centre International d'Etude des Textiles Anciens.
[1][2] According to Naomi Tarrant in obituaries for The Scotsman and Costume, Swain was "an immensely warm and helpful person, always interested in the ploys of younger people".
[1][5] The Scottish National Portrait Gallery said she was the first to notice that Scotland was "unusual in the number of private houses which still contained historic textiles.