My cousin's sister-in-law is a Celtic musician as well, named Ashley Davis. She's American but studied music in Ireland. She sang an original song called "Beannacht" (I think) for their wedding and also sang a very ethereal version of the Cranberries' "Dreams". She's very talented. Just figured I'd share her website since we're talking about Celtic Women singers:

http://daisyrings.com/

Hope you enjoy.