She was hired to sing, not to get on stage at a casino and knock Las Vegas, claim the advertising was wrong or use the platform to make political speeches.

If she wanted to sing a song about injustice or politics, I couldn't say they had any grounds.

Say you (Norm) hire me to play in a band at your wedding and I take some time between tunes to talk about leagalizing prostitution and gay marriage. Heck it's freedom of speech, you should appreciate that?

Personally I think preformers don't have any better grasp of the real world, including politics. Judging from past history and the wacko's that end up being stars, I'd say they have less credibility than some drunk in a bar. (which by chance is where you will hear people spouting politics as well.)

Go tell your employer that his place stinks, he's running it wrong and he's part of some government conspiracy. I'm sure you'll have a free speech case for the courts after you get fired...

That's what she did. That's what they did.