No, that couldn't happen to Queen Gina! She would be declared the Queen of Western Australia and gives everybody at least five minutes off their mandated hard working day to celebrate it!
No Federation? Well, as one of the primary drivers for Federal was defence and in particular, fear of the rise of Japan, I can't see WWII working out well for us. The US in particular would be placing a lot of pressure on the separate colonies to co-operate a great deal more and co-ordinate their defensive plans during WWII. The UK I can foresee being well, not unhappy, with such an outcome. They have always preferred that the colonies were "divided" and "ruled". Makes it harder for them to stand up to the UK on Imperial issues.
WWI would have been also an interesting problem. How would the ANZAC corps (and hence tradition) have occurred? While built on Gallipoli, it was really the Western Front, under Monash that cemented it in our zeitgeist. No united Australia, no ANZAC Corps, except perhaps under a British commander (the colonies would no doubt continue their childish squabbles even in wartime).
Alternatively, the furnace of WWI might well be what forges a common will, in Australia. The increasing fear of Japanese dominance in east Asia, could well be what brings the colonies together.
IMHO, Federation was inevitable. The idea would not go away and it is too sensible to die. It was largely just a matter of when, where and whom. You can give reasons why it didn't happen in 1901 but it would have happened eventually, Greg.