Morgan Llywelyn, was born December 3, 1937 in New York City. According to the celtic cafe website, "She calls herself "a historical novelist specializing in the Celtic culture...Morgan's books reveal lengthy bibliographies and have also been translated in a number of languages. ...." She resides in Dublin now.
We read about this prolific author (some 40 titles) that she has four novels optioned for movies: Lion of Ireland, (1980) Bard, (1984), Grania: She-King of the Irish Seas (1986),
and The Last Prince of Ireland: A Novel (1992). And also:
Morgan Llywelyn is also the only woman to have walked both the breadth and length of Ireland on her personal feet. From Malin Head to Mizen Head was 427 miles, walked at the peak of the hottest Irish summer in living memory. "It meant walking over 30 miles a day for sixteen days with no break," she says. "We raised a lot of money for charity...that sort of thing is very much a part of whatever I am." In addition to writing, Llywelyn is also Chairman of the Irish Writers' Union.
Some biographical depth is available from the website of her publisher, O'Brien Press:
Historian and novelist Morgan Llywelyn was born in New York City, but after the death of her husband and parents in 1985 returned to Ireland to take up citizenship in the land of her grandparents and make her permanent home there.
After making the shortlist for the United States Olympic Team in Dressage in 1975, but not making the team itself, she turned to writing historical novels exploring her Celtic roots. The most successful of these was Lion of Ireland - The Legend of Brian Boru, which was published in 1980 and has sold into the millions of copies.
She received the Novel of the Year Award from the National League of American Penwomen for her novel The Horse Goddess  as well as the Woman of the Year Award from the Irish-American Heritage Committee for Bard: The Odyssey of the Irish. The latter award was presented to her by Ed Koch, then-mayor of New York City....
In 1990 Morgan Llywelyn turned to writing for the young reader, with the publication of Brian Boru, Emperor of the Irish, a biography in the novelistic style, by The O'Brien Press, Dublin. For this book she won an Irish Children's Book Trust Bisto Award in 1991. ...
Here is a glance at the blurbs on her books:
Bard: The Odyssey of the Irish Celtic World of Morgan Llywelyn
"This is the tale of the coming of the Irish to Ireland, and of the men and women who made that emerald isle their own."
and After Rome (2013) : "Anarchy rules in Britannia as the Roman Empire collapses, and two men fight to build stable lives among the chaos."
We encountered this interesting author because she also wrote a short story, "The Cat with No Name" which is anthologized in Emerald Magic: Great Tales of Irish Fantasy (2001) a selection made by Andrew M. Greeley.