‘The show must go on’. It’s one of these clichéd sayings that are so overused that their real meaning becomes lost in the mists of time. But does the show really have to keep going on when the star of an opera breaks a leg onstage? Or when the concert hall’s lights fail three times on the trot (as happened at the Usher Hall last August) and music scores are plunged into darkness? As far as the seriously glamorous American mezzo-soprano Joyce DiDonato is concerned, the answer is a very definite ‘yes’, and she’s not just saying it. She’s been there and kept the show going in both scenarios.

Another theatrical mantra is, of course, ‘break a leg’, usually a throwaway remark to actors and singers before they go on stage. It’s meant to mean good luck, but for DiDonato it was the real deal when she appeared in the first night of Covent Garden’s Barber of Seville not long before her dramatic 2009 Edinburgh International Festival appearance. But even when a more normal reason, such as a holiday, might mean that the show can’t go on, DiDonato still pulls out all the stops to make it work. Looking forward to this year’s festival, she says, ‘I should really be on vacation at the time I’m in Edinburgh, but when my agent told me I would be working with Sir Charles Mackerras, it was an opportunity that I found difficult to say no to.’

It was perhaps not a surprising response as DiDonato’s last season debut as Donna Elvira in Mozart’s Don Giovanni at Covent Garden with Sir Charles was a knock-out success. Making a return visit to the Usher Hall, where electrics are now truly tried and tested, DiDonato takes the part of Idamante in a concert performance of Mozart’s Idomeneo. Sometimes sung by a tenor, but more usually these days a trouser role for mezzo-soprano, Idamante is the son of Idomeneo, King of Crete. ‘It’s the sort of piece which works very well in concert performance,’ says DiDonato. ‘Mozart gives you everything in the music and to stage it can be very tricky, and even detract from the opera.’

The combination of Mozart, Sir Charles Mackerras and the Scottish Chamber Orchestra, is one which not only DiDonato is anticipating with relish. Mackerras’ interpretations of Mozart operas are unparalleled and hugely popular. ‘It’s all the years of experience and expertise he brings,’ DiDonato explains. ‘As a younger singer, you really appreciate that. He knows exactly what he wants and how to shape it to the individual singer, which is really important in Mozart. What is most wonderful is that he is still making discoveries in the music. There’s a sort of childlike quality to him that brings a proper balance of respect and awe.’

It is not, however, only Sir Charles that has attraction for DiDonato, but the role itself. ‘It’s such a touching role,’ she says. ‘Idamante has this sense of sacrifice and duty, with adoration for his father. He’s really noble.’ But even without unanticipated hiccups, Idamante is not for the faint-hearted. ‘For the first ten minutes, it’s lovely, but then it’s terrifying. The opening aria is really treacherous and so demanding you just want to get rid of it quickly. As a musician, Idomeneo is a wonderful opportunity.’

DiDonato’s two EIF appearances also include a solo recital at the Usher Hall, with pianist David Zobel in which she sings love songs with a strong flavour of Italy. Last year’s experience in Edinburgh’s main concert hall has clearly not dented her enthusiasm for appearing there. ‘It was actually so funny, especially as it was one of the first things I did after the leg-breaking experience in London. Having survived that, I just thought, “This is nothing, it’s just the lights going out”. My job as a performer is to give a good performance. If there’s a problem to be solved, it’s not worth getting into a hoop about.’

Covent Garden and the leg was a different matter. Rosina is another highly demanding role, not only vocally but physically. ‘On opening night, it was a matter of survival,’ says DiDonato ‘I did it when on stage, just after my opening aria, so there was still two hours to go.’ Never having broken any bones in the past, DiDonato actually thought that she had merely sprained her leg, relying on adrenaline and sheer willpower to get her through the rest of the opera: ‘It didn’t cross my mind that I’d broken it.’ For the rest of the run, DiDonato performed from a wheelchair, a highly unusual arrangement that not surprisingly required significant improvisation. ‘We obviously hadn’t rehearsed that way, but it was quite exhilarating and I know the role pretty well, and felt I knew how Rosina would react.’

Such a positive attitude in dealing with adversity may well stem from DiDonato’s roots. Growing up in Kansas City where practical stoicism could have been invented, she followed a fairly conventional path to the stage, singing in church choirs, high school musicals and studying at college to be a music teacher. ‘Then I got sidetracked. I just fell in love with being on stage and the whole thing of music and theatre.’ It’s a pretty serious love affair as learning roles is intensive, exhausting and, taking up to three years to get fully into some of them, very time-consuming.

‘You’re also constantly on the road as a singer,’ she says, ‘and have to work very hard to keep a balance of the job and real life. Not being settled anywhere is probably the biggest challenge.’ And that’s in addition to breaking bones, dealing with electrical faults and not getting a holiday. The latter, however, is one which can be dealt with and DiDonato insists, ‘I’ll be in vacation mode from the 23rd.’ Sounds like she could do with it.

Idomeneo, 20 Aug, 7pm, £10–£40; Joyce DiDonato/David Zobel, 22 Aug, 8pm, £8–£32. Both performances at Usher Hall, Lothian Road, 0131 473 2000.