I think the poster was hoping there was a law that would allow her to say, No, I'm not going to accept being demoted, and the employer would be forced to say, Oh, okay, we'll leave you in your old position then.
No such of a thing. As someone said above, her options are to accept demotion, quit, or be fired. There is no law anywhere in the US that is going to force the employer to leave her where she is if they don't want her there any more.

