I've dug out the photocopy of the liner-notes of Mary O'Hara's Decca recording " 'Monday Tuesday' and other children's songs", which John Moulden sent me when I was enquiring about the title song (translation of Irish title 'Dia Luain Dia Mairt'). Now I can give you more precise dates than I did on 30 Jan.
According to the album cover, Mary O'Hara married Richard Selig in 1956. She was 21 years old at the time. Richard died of Hodgkin's disease only 15 months after the couple married. His widow spent the next four years actively recording and touring and performing. Then quite suddenly, she left it all for a "strict Benedictine monastery in England" and she "never intended to play and sing again". But before entering the convent, Mary recorded enough material for three albums, subsequently released under the the titles 'Mary O'Hara's Ireland', 'Mary O'Hara's Scotland' and 'Monday Tuesday...'. She spent 13 years in the monasterybefore resuming her career; I gather the years of seclusion would have been around 1962-1975.
An internet search informs me of a chapter profiling Mary O'Hara in "Musicians" by Leslie Strudwick, one of a series of [2oth century] "women in Profile" published by Crabtree Press. The other musicians featured in depth are Liona Boyd, Midori, Ethel Smith, Vanessa-Mae and Mary Lou Williams. There's also some information on Cindy Blackman, Jane Ira Bloom, Laurie Frink, Ofrah Harnoy, Sharon Isbin, Wanda Landowska, Natalie McMaster and Fr‚drique Petrides.
I hope, Sandy, that you succeed in getting in touch with Mary O'Hara again.