I don't think she should withdraw either. I would find it very difficult to believe that any of the finalists haven't put out the word to family and friends to vote for their images, via FB or otherwise.
If it's open to popular vote, the photograph voted most popular wins.
I'd be intrigued to see how this will be dealt with by the Australia Day Council. There is nothing explicitly stated about family/friends voting for one's image, however there is a general "if the ADC feels the competition can't be run as intended we'll disqualify" clause in the rules which could cover this, but how bloody churlish would that be on the part of the ADC if that's how they chose to proceed. It's not as though Bec posted herself on EB (which has to be where a large number of the votes came from) saying "HERE'S MY PIC!! VOTE FOR ME!! I NEED $5K!!!"
I would argue that the ADC cannot possibly prove that people only voted for Bec's image because of the flood donation, rather than the undeniable professional and emotive qualities of the image.
And Damien is definitely a douchebag