We were scheduled to play early in Las Vegas so we told Mags she could watch us while we played.
But then, she wanted to know where on the stage she would be standing...and playing. This conversation happened 5 minutes before we went on. So, instead of leaving her mid diva-tantrum, we set her up to seem like she was part of the band.
She had a special chair, stage left with a mic stand and microphone (not plugged in) and a tamborine. 
She, very seriously, played percussion (and occasionally sang) throughout the whole set.
Then, as a special treat, we let her join us for real on the last song. We hope she had as much fun as we did. And I'm hoping this was only an occasional visit to the stage for her-even though she is a great tamborine player.