I think the GG will have to do what the Prime Minister asks. We can't expect her to over-rule the top elected official in the country. If she does as he requests, she will appear cautious, prudent, and perhaps, to some, timid - but if she were to deny his request, she would leave herself open to the charge of partisanship, and would thus bring discredit to her position. And that would be the sort of thing that could provoke a real constitutional crisis.