Normally we don’t do this … if someone doesn’t come in on a solo, the solo is just missing. It would be rude, for instance, for me to play the principal oboist’s part without her permission and encouragement. (If she suddenly had a coughing fit or something I suppose she might ask me to play … but that’s never happened and I’m happy about that!) But in this case I read that the conductor yelled for someone to sing the soprano solo in Aida because the soloist was AWOL. A violinist stood and did the job.
And she did it well.
Brava, Jennifer Lindsay. I’m impressed!