I suppose in theory she could claim that she was entitled to be paid the gate based on purchased tickets, and that the decision to pay back people walking out was a transaction made by the management which didn't affect that...

Would it be any different in legal terms if it had been an audience walking out because, for example, a performer expressed other views that people found offensive? Which could include a very wide range of things.

I'd think for that a performer would need to keep on performing at least until there wasn't a single person left in the audience. Which doesn't appear to have happened in this case.