Simple Verse has been supplemented for Saturday's Ladbrokes St Leger at Doncaster.
The daughter of Duke Of Marmalade has won three of her last four starts, most recently running out an impressive winner of a Group Three prize at Glorious Goodwood.
The three-year-old had the option of taking on her own sex in Thursday's DFS Park Hill Stakes at the Town Moor track, but connections have decided to bid for Classic glory against the boys.
Trainer Ralph Beckett said: "She worked very well on Saturday, she's had a number of tests done and all those came back A1 and we feel it's the right time to have a go and roll the dice.
"We're very much looking forward to it."
Simple Verse will bid to become the first filly since User Friendly in 1992 to win the St Leger, but Beckett has come close to winning it twice with two Oaks winners, as Look Here finished third in 2008 and Talent was runner-up in 2013.
Simple Verse is among just eight horses confirmed for the season's final Classic.
Aidan O'Brien has a formidable hand as he bids to win the race for a fifth time, with impressive Irish St Leger Trial winner Order Of St George joined by stable companions Fields Of Athenry and Bondi Beach.
Bondi Beach is set to cross swords once more with the William Haggas-trained Storm The Stars, who was a narrow victor when the pair clashed in last month's Great Voltigeur at York.
The home team is made up by David Brown's Medrano and Proposed from Richard Hannon's yard, while French trainer Mikel Delzangles has left in Vengeur Masque.
