Here, after all, is an age-old tale of how a young woman went to the ball as a stranger before leaving all about her dazzled before she disappears. So it has been with O'Riordan's three-year tenure in Perth, which has seen the Cork-born director arrive in Scotland as an unknown quantity and pretty much revitalise one of the country's oldest producing houses with some bold programming and even bolder results that have increased audiences, drawn critical praise and won awards.
For her final production, O'Riordan persuaded playwright Alan McHugh to re-jig his original script so the action now takes place in a theatre rather than a stately home. Coming on the eve of the building going dark for two years as it begins a £14 million redevelopment, this is O'Riordan's way of saying goodbye to the theatre she has called home for the last three years.
"I am deliberately referencing the fact the theatre is closing," O'Riordan says. "Not overtly, but it is just a little nod to how fond I am of Perth Theatre, and of theatre in general and all the people who work in it. I didn't know I was leaving when we decided to do that. It was more about the theatre closing, and trying to remind the audience how important this theatre is."
The announcement of her imminent departure from Perth to take the helm of the Sherman Cymru theatre, Cardiff, in February 2014 may have been good news for Wales but, on the eve of the theatre's closure, for Perth it looked like the fairytale was over. This was especially the case when it was announced a week later that Jacqueline McKay, chief executive of Horsecross Arts, the body in charge of both Perth Theatre and Perth Concert Hall, had suddenly stepped down from her post for reasons that have yet to be made clear.
Anyone of a superstitious persuasion might suspect that the curse of Macbeth, which O'Riordan had just directed, had fated such a turn of events. As O'Riordan points out, however, the two announcements were unconnected, and their close proximity was a coincidence.
"Genuinely," she says, "the two announcements were not connected in any way. I was approached for the Sherman job. I wasn't looking, and had no desire to leave, but the Sherman approached me a while ago. The process of these things takes so long, so it was not as if it happened overnight.
"I had it in my head when I arrived here that I would be in Perth for five years, and saw it very much being a step on a journey. While Perth Theatre being closed is a very exciting time, I do need some kind of stage to do my work, and when the Sherman approached me, it felt like the right thing to do."
The decision to leave Scotland now, she admits, has been a tough one. "I felt I had just found my groove," she says. "I love it here, and have had three of the best years of my theatrical life here. I feel I have made friends and connections with people in Scottish theatre who I want to work with in Wales.
"The first co-production I did here was (Conor McPherson's play) The Seafarer with the Lyric in Belfast, so that was me bringing all my Northern Irish connections to Scotland, and now I am taking those with me to Wales along with all my Scottish connections, and I hope to do co-productions between the nations that way. I like the vibe here. We showed with The Seafarer that you can co-produce with theatres from different countries involved."
She says she is "cursed with ambition" and this has shown in her work at Perth, from her opening production of Shakespeare's Twelfth Night in 2011 through to a look at Frank McGuinness's play Someone Who'll Watch Over Me, her award-winning production of The Seafarer, and this year's mystical and very male take on Macbeth.
Ask what she is most proud of during her time in Perth however, and O'Riordan answers: "My team. They are by far and away the best team I have worked with. The reason I have made good work here is because I have had that kind of support. And that is hard to leave, even though I hope I am leaving on a high."
O'Riordan is full of praise, too, for Jane Spiers, the then chief executive of Horsecross who took a chance on hiring someone outwith the immediate Scottish scene. Any advertisements for O'Riordan's replacement will not be placed until a new chief executive for Horsecross is in place. One only hopes whoever makes the new appointment will apply the same sense of vision as Spiers did when appointing O'Riordan.
O'Riordan seems genuinely sad to be leaving Perth, and her conversation is tinged with emotion. One suspects, however, this will not be the last Scotland's theatre scene sees of her work.
She was due to direct something at the Tron, who co-produced Macbeth with Perth, but the move to Cardiff has put the kibosh on that. She also has a big project in the pipeline, which she can't talk about, not even to say if it is taking place in Scotland or not.
Whatever happens next, both for Perth and O'Riordan, it is clear she has left her mark in Scotland's theatrical landscape.
"I have worked very hard," O'Riordan says. "For the last three years this theatre has been my life. The way I work is all or nothing, which makes it sound like it was all about labour, but there was an awful lot of love as well. I hope I have brought a bit of rock 'n' roll to Perth, and I hope the next director of theatre here can bring something new to the table, and make Perth Theatre more special than it already is."
Cinderella, Perth Theatre, December 6-January 4