The 13-year-old performed her power pop-anthem Speak Up, at the Tbilisi Sports Palace on Sunday local time, walking away with Australia's highest-ever place in the junior leg of the competition.
"We congratulate Isabella on her extraordinary achievement - she should be extremely proud of her performance and her outstanding result," head of ABC children's television Michael Carrington said in a statement on Monday.
"Up against some amazing competitors, she delivered a spectacular performance."
Isabella was accompanied to the competition by her three backing vocalists Mia Papzis, Tiana Carbone and Jessie Eilers, who also travelled from Melbourne.
Sixteen countries took to the stage at the annual contest, with 14-year-old Russian Polina Bogusevich taking gold with her song Wings, which scored 188 points from juries and online voting.
