@C152
Was she wrong though? The audience are encouraged to sing during Mama Mia and similar performances - isn't this much the same thing? (Obviously you wouldn't be singing along during a play, but this was a muscial - I thought that was considered part of the fun of going to a musical?) Either her behaviour must have been sigificantly more distracting than she thought, or the ushers overreacted; possibly a bit of both from the limited information available.
I've seen Mamma Mia twice - the audience was only encouraged to sing along during the last song from what I can remember. I love musicals, I've seen:
Wicked
The Lion King
The Bodyguard
Thriller
School of Rock
Legally Blonde
Tina
Kinky Boots
Matilda
Jersey Boys
Waitress
Beauty and the Beast
Everybody's talking about Jamie
You don't sing along unless specifically encouraged to, there are sometimes signs saying something like "please don't sing along". When I saw Thriller and Tina, a couple of people near me got asked by the usher to be quiet because they were singing along, and they stopped. When I saw Matilda there was a drunk woman sitting behind us who was being very rude and disruptive, they asked her to be quiet several times and eventually kicked her out.
People don't pay £20 - 200 to hear Dot signing along.