Only fourth behind More Mischief at Newcastle last time out, she appeared to relish the soft ground and travelled with zest throughout.
William Haggas, who had earlier secured the Listed race at Ascot with On Her Toes, was running out of options with the four-year-old to gain black type but she delivered in style.
Paul Hanagan had her close to the pace and the first-time cheekpieces appeared to work their magic as the 7-1 chance saw off Ajman Princess by a length and a quarter, with favourite Playful Sound in third.
"The cheekpieces helped but the ground as well, she seemed to really appreciate it, she skipped through it," said Hanagan.
"I rode her last time on the Tapeta surface at Newcastle and that just felt a bit quick on her but it was one extreme to the other today.
"She was very game in front in today. After riding her last time I knew she stayed well so I wanted to be positive."
Alison Begley, representing the winning owners Al Shaqab, said: "She's going to stud in Australia now."
Tim Easterby is already thinking of another St Leger after the first-time-out victory of two-year-old Wells Farhh Go in the Best One And Xtra Local Novice Median Auction Stakes.
Nibbled at in the market before the off, he was still sent off 16-1 against Roger Varian's 2-1 favourite Laugh A Minute but was last at halfway.
By Champion Stakes winner Farhh out of a Galileo mare, he quickened up in fine style, leaving the Newmarket raider for dead in the final furlong to win going away by two and a quarter lengths.
Easterby, who won the world's oldest Classic in 2002 with Bollin Eric, said: "This could be a St Leger horse. He's very good, he'd been working well in the mornings.
"Being by Farhh we thought he'd be OK on the ground.
"I'm just annoyed I didn't keep a share in him like the person I bought him off told me to."