Thornton went straight to the lead on Sugar Boom ($5) who ran the field into the ground before beating Oh Five Glory ($7.50) by three-quarters of a length in the Listed Mode Plate (1200m) at Doomben.
Euro Belle ($61) was a long neck back in third place.
Thornton moved to Queensland for a three-month stint with trainer Steve O'Dea but has swept all before her and has decided to stay in the north.
Sugar Boom was her 25th metropolitan winner of the season and she is now third on the senior riders premiership.
The win gave trainer Tony Gollan a Doomben treble after earlier scoring with Man To Match and Le Palmier.
"Sugar Boom goes really well for female riders and Steph is the best around at the moment. She won on Sugar Boom at the Sunshine Coast and I had no hesitation putting her on today even though she couldn't claim," Gollan said.
"Sugar Boom is a much tougher filly this campaign. She has really bloomed over her break and I think she can now live up to her early potential."
Gollan will now add Sugar Boom to his team for the Listed Gold Edition Plate at Eagle Farm in a fortnight where he could have half a dozen runners.
Thornton was thrilled to score her first stakes win in Queensland and declared she was here to stay.
"I am getting a lot of support from trainers and I can make the most of my allowance in the coming months," she said.
"Sugar Boom is a nice filly to ride and she really found something on the corner."
Trainer Peter Hulbert was thrilled with Oh Five Glory's return to form with her second.
"That was more like it and a bit a rain to take the fire out of the tracks would also help," he said.