Upon intermission, I asked her if she noticed all the people seated in front of us turning around to stare at her and thereafter suggested that her whispering bothered them. She was shocked that this behavior would be considered rude and then stated that it was their problem. She proceeded with this through the end of the play. I’m shocked no other patrons confronted her. Based on this fact, I wonder if perhaps I am wrong and overly sensitive. Who is right?
Answer: Oh my God, you’re right. On no planet, no parallel dimension, is singing along with a musical from the audience considered good theatergoing etiquette. A few years ago a woman was thrown out of The Bodyguard musical for doing exactly what your friend did.
Obviously there’s nothing to be done about it now, aside from committing to never seeing a live musical with her again, but if you simply want the rush of being told you were right by a stranger on the internet, allow me to grant you that rush: You were right, and your friend was rude.