Take her featured soundtrack performance in Ridley Scott's 2010 movie Robin Hood, starring Russell Crowe and Cate Blanchett - the kind of mass exposure most traditional musicians could only fantasise about, but which MacInnes very nearly, albeit innocently, passed up.
Scott had happened across the South Uist native through her acting and singing roles in the 2007 Gaelic film Seachd: The Inaccessible Pinnacle, and assigned someone to track her down.
MacInnes says: "I'd taken a couple of years out before my youngest was born, and was back in South Uist with the new baby - away off completely in another world - when some random guy got in touch on Facebook, saying he wanted to hire me for a Hollywood film. So of course I just deleted it, but he kept sending more messages. I even replied saying I really didn't think it was me he was looking for, but eventually he convinced me it was genuine.
"Then they wanted me to record in LA, so I was getting all excited about flying out there, when I realised my passport had expired. There wasn't time to renew it, so we ended up recording in London. But at least I got to sing at Abbey Road."
MacInnes grew up in a Gaelic-speaking household, absorbing music from a variety of sources. "It was a very quiet, gentle upbringing, in a very remote and beautiful place," she says. "I had uncles who were pipers and box players, and I'd hear Gaelic singers at community concerts. My mum sang in church, so Catholic hymns were a big thing, too - I still love a good hymn - plus the odd country and western record."
But she didn't begin thinking of herself as a singer until her late twenties. "I always enjoyed singing, but I used to be really shy about it - not you'd believe it now," she says, alluding to the self-evident delight she takes in performing today.
After leaving school, she studied textile design before moving to Glasgow and being "waylaid" into television, landing a job on the erstwhile STV arts magazine show, N. This coincided with the early days of Gaelic broadcasting, in which she has worked ever since, as an actress, presenter and voiceover artist.
"I've sung in Robin Hood, and I've sung for the Pope," she says (the latter occasion being Benedict XVI's Glasgow visit in 2010), "but still my greatest career moment has been doing the voice for Mummy Pig in Peppa Pig on BBC Alba: my four-year-old was just delighted."
This variety of professional hats has also provided the flexibility to fit in with bringing up her three sons, as well as gradually instilling the confidence to step into the spotlight as a singer. "I used to much prefer acting because you had the character and the script to hide behind, whereas singing felt so much more personally exposed. But just through getting used to performing, I started to feel more comfortable when I did sing in front of other people."
One such occasion occurred back around 1997, after a day's filming of the innovative Gaelic music programme Tacsi, which MacInnes was presenting, and whose musical director was Capercaillie accordionist Donald Shaw - now also Celtic Connections' artistic director.
He says: "Because I only knew her through that show, I saw her very much as a TV person. But someone persuaded her to do a song in the bar one night, and I was just utterly gobsmacked. I think I spent the rest of the night trying to convince her to stop whatever else she was doing and just sing.
"There's a really strong Hebridean style to her voice, and also something very lived-in, kind of bluesy and really soulful - almost like Nina Simone, if she sang in Gaelic … Kathleen's style is very much her own."
Shaw has been a key supporter of MacInnes's career ever since, latterly via several high-profile shows at Celtic Connections, a profile also boosted not only by Robin Hood but by her two albums to date, 2006's Òg-Mhadainn Shamhraidh (Summer Dawn) and 2012's Cille Bhrìde (Kilbride). The first saw her voted Gaelic Singer of the Year at the Scots Trad Music Awards, while the second - featuring a guest appearance from US banjo legend Béla Fleck - won Album of the Year, together with a Radio 2 Folk Award nomination.
Following her two sellout shows at this year's festival - under her own name next Sunday and, last Friday, as half of the Urban Teuchters with fellow South Uist singer Sineag MacIntyre - plus a string of guest appearances, MacInnes has a busy year ahead of her. As well as a leading role in new Gaelic TV drama Bannan, produced by Chris Young, who also produced Inbetweeners, she also features prominently in composer/producer Jim Sutherland's ambitious forthcoming project Struileag/Shore To Shore, an exploration and celebration of Gaelic culture's worldwide diasporan journeys, to be premiered during the Commonwealth Games.
Sutherland says: "Kathleen's voice seems to come from the far distant past, but at the same time communicates incredibly vividly in the present. The sense of emotional narrative she brings to a song is just exquisite; for me she's one of the greatest singers in Scotland - in any language."
Kathleen MacInnes plays the Mitchell Theatre on January 26, 8pm