I'm not an expert on administrative law but I'll give you my take:
I don't think the purpose of this case is to make a statement. It's a way to challenge the legitimacy of the curfew through the judiciary.
The state of emergency certainly doesn't mean the rule book goes out the window. What it does is grants the government certain emergency powers. The power in question here is provided in section 200 (1)(a), the power to,"restrict the movement of any person or group of persons within the emergency area." Prima facie the curfew seems to be a perfectly reasonable use of this power. There is a provision in this section which states that use of these powers must be authorised by the CHO.
Where it gets tricky is that there are a bunch of provisions in this Act about evidence-based decision making, not making arbitrary decisions and using the least restrictive measures practicable. The curfew in particular seems like it can be challenged along those lines. My understanding is that Sutton admitted publicly that he did not recommend the curfew. Unless the government can show that it had some form of evidence to suggest that the curfew was necessary as a public health measure, the courts might determine that it's not legitimate. If the aim of the curfew was only to assist law enforcement then the judges may have to decide whether that's a reasonable measure for protecting the public health.
It seems pretty obvious to me that the plaintiff in this case won't be awarded any damages. I'm struggling to see how a curfew could be the main cause of loss of revenue for a cafe. I imagine they know this and don't really want to sue the government here; they just want to get the curfew thrown out.
Perhaps she is positioning for a run at preselection.... even if she fails, she can run with ‘at least I did something’ line.