“Life is good to me. So I can’t complain, but I do often,” she laughs raucously as we catch up for the first time in nearly two decades.
“You know, I don’t believe I have ever played Dunfermline in my entire 35 year career as a musician, not even with Goodbye Mr Mackenzie.”
The singer’s last performance in the Capital was in 2018 when Garbage brought their 20 Years Paranoid tour to town, celebrating the 20th anniversary of their second album, Version 2.0, this time around, fans can expect a few surprises.
“It’s an entirely different set from the last time we visited Scotland,” the singer promises.
“It’s a much more broad selection from all the records, including some obscure B sides and some of the songs that have been released solely on vinyl.
“We’re looking forward to it and are all enjoying this set because there are some songs we haven’t played in over a decade.
“I think, if you are a fan of the band, you will come away quite satisfied. You’ll get something from every record.”
Fifteen years ago, it was a very different homecoming concert that shone the spotlight firmly on Shirley and Garbage, when they were invited to play the Ross Bandstand to mark the opening of the Scottish Parliament.
“That is the most important show that I have ever played in my life,” says the 52-year-old.
“It’s the one that means the most to me and the one I will always remember. I feel like, when I’m on my death-bed and flash back through my life, that will be the most memorable moment; the greatest honour of my entire career.”
The significance of the day is something of which the singer, who reflects she had “an incredible childhood, very light and breezy and very sweet” growing up in the “incredibly innocent” Scotland of the Seventies, is obviously proud.
“My country has great significance to me.
“I’m not a great believer in the management of people. I’m not affiliated with any political movement or politician - they all disappoint me,” she laughs.
“So I never put enormous faith in the development of a Scottish Parliament necessarily at that time. I thought, ‘Let’s just see where it goes’.
“I remember we sang The Beatles’ Don’t Let Me Down because I was aware how rhetoric is so easily voiced but actual true change is rare.
“Politicians all over the globe let us down left, right and centre, but I felt that was a day for the Scottish people, so it was really important to me.”
Although Shirley now lives in LA and spends much of her time travelling, there’s no doubting her love for Scotland.
“I miss it, of course I do, but I’m also very lucky that I get to travel the world and see other cultures and other ways of living and to experience other philosophies and outlooks. That also has been precious to me.
“The more you travel, the more you discover people are exactly the same the world over.
“So much is made of our tiny little corners of the planet, but we all want the same thing and I don’t believe any human being should ever be considered illegal. It’s such a hideous term.”
Famous for her straight-talking, Shirley has never been shy of saying what she thinks.
“It has been a blessed tool in my arsenal when going out into the world, and things were easier for me than for other women because I had that at my disposal,” she says.
“I had an incredible education at a state run school thanks to the Scottish Government at the time, so I am articulate and relatively self confident.
“When I was younger I didn’t take any shit and I still don’t, I was encouraged by my parents not to, but not everybody comes from a background with loving parents and supportive institutions.
“A lot of people are so disadvantaged now and it’s those women that I really want to ensure have an easier ride.”
At the vanguard of the ongoing fight for women’s rights, particularly in the music business, the singer who started with Goodbye Mr Mackenzie and Angel Fish before taking the leap across the Atlantic to join Garbage, admits that in her younger days she was oblivious to much of the inequality around her.
“It’s only as I have got older and had the luxury of time to reflect on how the world actually is that I have realised.
“As a young woman I was too busy trying to forge a career and was oblivious to the fact that the board game wasn’t stacked in my favour.
“I was completely oblivious to the fact women operate at a disadvantage in our culture.
“As I’ve got older, I’ve become more and more outraged, not so much for myself because I feel it’s pretty much too late for me - I have an amazing career and, despite some of the setbacks I may have encountered as a woman, I have flourished.
“But I am keen to try and ensure the generations of young women behind me get it a little bit easier than I had it and certainly easier than the generations before mine.”
Voicing those opinions have led to Shirley being trolled on Social Media platforms.
“Any person, irregardless of what they do for a living, must be prepared for push back if they put an opinion out to a social media platform,” she says bluntly.
“It doesn’t matter what you say, there’s always a troll out there with nothing better to do than be a fly in your ointment.
“To be honest, I don’t really take it too much to heart but every now and then, if you catch me on a bad day, I just want to push back.
“I try not to and have become less and less interested in engaging with trolls,” she says, adding with a laugh, “I just used to find it amusing, an enjoyable sport, but now I find it boring.”
With three bands, four albums, a Bond theme (The World Is Not Enough in 1999) and a lead role in the sci-fi series Terminator: Sarah Connor Chronicles to her credit, Shirley, who started performing with the Edinburgh Youth Theatre in the Eighties confesses there was never any real plan.
“I think I’ve found my calling. I’m in rude health and I think that’s because I’m doing exactly what I’m supposed to be doing,” she says.
“Looking back now, I can’t believe I’ve had the privilege of being a musician for 35 years. I’ve done all kinds of things I never imagined I would as well as seeing things that have beggared my own belief but it was all totally haphazard.
“Bond was an immense honour, it’s such a precious franchise and to be part of that cinematic history is really something quite special.”
She thinks for a minute and adds, “I’ve had an extraordinary career, it’s been like patchwork. I’ve never had any grand plan and never, in my wildest dreams, imagined I’d still be here making music and touring.”
Garbage play Dunfermline Alhambra on 17 July, 7pm, £35, www.ticketmaster.co.uk