But employment contracts are typically “at will”, meaning that either party can change the terms at any time, but the other party can separate rather than be bound by the terms.
The haziness in this situation is that the restaurant didn’t come out and say point-blank: “this is a change, we’re enforcing it, agree or walk”. If they had, they’d be legally in the clear, as far as I can tell, even if they risked some ill will.
But after she complained, they allowed her to wear the old uniform but then proceeded to act in an allegedly retaliatory fashion — that puts the legal situation in a much murkier light.
Given she found an attny to take the case, and she’s a waitress, (meaning I doubt she put up a $3000 retainer and paying 200-500 an hour for them to work on the case) I suspect the attny that took this case feels pretty confident they will win.