I'd ask Rockerball.
I'd guess not asking for the issue of the writs leaves open that tiny possibility that the dates could move again. Nobody is daft enough to think she's announced the date and parties won't start campaigning until the Crown "approves".
What I've observed is that, atleast here in Australia, the Premier would usually go to the governor to get the writs issued then announce the election. It's pretty much just a formallity that the writs are issued when requested. (Same thing with the Prime Minister and the Governor-General)
I'm fairly sure there is some law on the books that allows the local government elections to be moved.
And finally, the campaign started prior to the announcement any way.