Well, I'm not the best since I don't know the specific details, but the short version is that after a series of
highly unpopular decisions, and low opinion polls, grumbling in the labour party finally reached critical mass and Rudds supporters pushed for a vote in change of leadership. Sentiments in the labour party have never been good since Gillard stood against Rudd, and ousted him as Prim Minister, and they lost a lot of standing with the public.
TBH the whole situation politically here is pretty stupid, neither party leader is all that popular (I may be a bit biased against the Liberal party from all the feedback from my gay friends, Abbot is a bit of a bigot), Rudd somehow still has quite some popular support in the public, he is pretty charismatic, especially in comparison to both Gillard and Abbot. Honestly I doubt Labour will win an election, so this whole thing was probably just the final death throws for a Labour government. (Which will suck for the new broadband network, Labour is giving FTTH Liberal FTTN and shitty wireless).
Apparently she was voted out unanimously to.
Result was 57 to 45, actually.
She's retiring to, along with a few of the other party folks.
edit:
http://www.abc.net.au/news/abcnews24/ new live feed, speech's and stuff.