It was finally published in 1985 by Oxford University Press, translated into five languages, and is still considered a classic of children's literature.
Her mother died when O'Shea was a small child, and she and the other children were brought up by her older sister.
In 1971 she worked on a sketch comedy show for Granada Television called Flat Earth, but this was not successful.
By the early 1970s she began writing The Hounds of the Morrigan to please herself and family and friends, with little expectation of getting it published.
[7] In poor health by the time of that novel's first sudden success, she completed only a few chapters of the unpublished sequel in the subsequent decades, although her obituary in The Guardian calls these "brilliant".