Around the time she was getting started with Celtic Woman, Máiréad did some guest appearances with Secret Garden. On their Earthsongs album, Máiréad featured in a couple of tunes ("The Reel" and "Daughters Of Erin") along with Secret Garden's violinist, Fionnuala Sherry.
You can hear these tunes on YouTube:
The Reel:
https://www.youtube.com/watch?v=0Th4s0edbbsDaughters of Erin:
https://www.youtube.com/watch?v=q5_qFUMpjy8