So if we talk about standards, "my boss can call me out of hours when it is convenient for them and I will make a spot judgement about my availability" appears to be the standard you work to. Which is cool. A little looser than my preferred standard but hey; everyone is a little different. But the law now seems to be that this is illegal and you can launch some sort of action against your company for engaging in this activity. With, for a brief moment, criminal penalties for the the people involved. That seems to me like either a stupid law or a poorly thought out one.

And I'd encourage your boss not to do that if I were you. It was already bad practice and there isn't any point in her taking legal risks.