She has just been crowned Donegal Person of the Year -- she is only the fourth woman to be given the award in 36 years. "The people who normally get it are usually long established, from a more conservative situation," she says with slight wonder. "I like the idea of them reaching out to the arts."
Mairéad (47) hesitates to consider herself an establishment. Her career trajectory has been remarkable, transporting her from a fiddle-playing teenager in Gweedore to sell-out concerts in the Sydney Opera House and the Hollywood Bowl. "The night we stood in the Hollywood Bowl," she remembers, "all I could think was, ' The Beatles played here!'."
But then, for Mairéad, the journey has been much more than geographical and professional. That quarter of a decade has encompassed great love and great sorrow.
Mairéad was only 22 when she founded Altan with her then husband Frankie Kennedy. The pair had met when Belfast native Frankie came to Donegal on a summer trip and spotted a gorgeous blonde 15-year-old playing fiddle at a session. Four years later -- and a crash course in learning the flute to impress Mairéad -- they were married.
They were both trained as teachers but soon took a full-time risk on their burgeoning performing career. Altan released their first album in 1987 to instant acclaim. By 1994, they were players on the global stage. They were fourth on the Billboard world music charts that year and, in an unprecedented signing of a trad band by a major record label, were about to get on board with Virgin.
It should have been Altan's most glorious year. Instead, 1994 is etched deep on the band's soul as the year they lost Frankie. He had been diagnosed with a vicious form of bone cancer in 1992 but had been in remission. Two years later, it came back with doubled aggression and he died that September.
Mairéad's voice softens when she speaks of that time. "I grew up very quickly when poor Frankie passed away," she says.
Before he died, Frankie had insisted that Altan continue without him. It was to be his last great gift to Mairéad, who considers touring with the band to have been her saving grace in the dark months that followed. "After Frankie passed away, it was very good for my head because it gave me something to do, a point in my day."
Other voices have dedicated songs to Frankie's memory, including past collaborators and friends Enya and Luka Bloom. But it is Mairéad's haunting vocals on a song called Time Has Passed, on Altan's 1997 album Runaway Sunday, that remains the most poignant elegy to her late husband. A jig she composed, called A Tune For Frankie, appeared on the previous year's Blackwater -- a specially arranged version is included on the 25th anniversary album.
"Music is a great healer," says Mairéad. "It sounds like a cliché, but it is. Words sometimes can't describe something that goes to a deeper level, and it's helped me through an awful lot."
None of this is said with melancholy. There is something intensely warm and joyous about Mairéad. She also speaks kindly of everyone who has passed through her life. Although her second marriage, to Altan accordionist Dermot Lynch, ended after eight years in 2007, they still work together amicably.
"You have to be sensible about it," she says of the split. "It was a hard thing but life's too short. I think I learned that from losing my first husband. He was nearly 40 (just 11 days short of his 39th birthday) when he passed and I realised that life is like a feather.
"Then when Dermot and myself weren't getting along, I just thought, 'Why? Why bother?' It's to do with quality. Every minute to me is important. I don't claim to know everything but I do think that you have to go for the plusses."
One of those plusses is six-year-old Nia, her daughter with Dermot. I thought Mairéad had taken a detour from Monaghan to Dublin for our interview, but she actually went home to Donegal last night. "I have a little one," she smiles, "I promised her I'd be away for two sleeps. If I was away a third sleep, I'd be dead."
It is very important to her that Nia grows up surrounded by the language and countryside that has inspired Mairéad. She lived in Dublin for a long time, but now she and Nia live in a house built of local sand and stone, the stunning Errigal mountains its backdrop. "I brought her back up here when my father [the legendary trad musician Proinsias O Maonaigh] was passing away and they got to know one another."
Altan's music is intensely rooted in Irish culture, but it has transcended the boundaries one would expect to limit a trad band. They are in huge demand in the States, Europe and Japan.
"Japan is a very good indicator of how the music translates to people who don't have any connection to the country," muses Mairéad.
It's not just the Japanese who adore them. Bill Clinton has had them play for him -- twice -- and President Mary McAleese requested they accompany her on several State visits, to Greece, Korea and, of course, Japan. They have recorded with Alison Krauss, Bonnie Raitt and Ricky Skaggs -- and one Dolly Rebecca Parton. On her 2001 bluegrass album Little Sparrow Mairéad's father translated The Sweet Bye and Bye for Dolly. "She liked that idea, because she says her people stemmed from over this way and Scotland," says Mairéad.
It would be lovely to sit and listen to her soft Donegal burr all day but she has to go. "I will be home again by 3pm," she says happily. Mairéad Ni Mhaonaigh might be a global ambassador for Ireland, but her heart will always be firmly in Donegal.