A dual Guineas winner, she also claimed the Coronation Stakes at Royal Ascot and then successfully stepped up to 10 furlongs in the Nassau Stakes at Goodwood.
There had been rumblings she might take on Churchill in the Irish Champion Stakes but O'Brien has decided to keep her against her own sex.
He said: "She's brilliant over a mile and she got a mile and a quarter the last day. She might even get further but she's a great filly and she's progressed with every run.
"The sky is the limit with her. We really don't know where she'll end up and when she will stop improving. She's changing physically every week so she's amazing, really.
"She'll come on for the run, with the idea she can have a strong autumn campaign."
O'Brien also fields Roly Poly, a dual Group One winner who landed the Prix Rothschild at Deauville last time out, Hydrangea and Rhododendron.
The Ballydoyle handler told At The Races: "Roly Poly is a solid filly. She's danced every dance this year and has improved with every run.
"Her last run was exceptional and she's on the crest of a wave. She'll be right there at the end.
"Hydrangea does all her work with Winter so is in the same shape.
"Rhododendron had a mishap in France. Maybe some stuff didn't work for her and she bled, which she's never done before or since.
"Everything has been perfect with her since. She's just ready to start back and we'll be delighted if she runs a nice race.
"She'll have options like the Breeders' Cup for fillies, which is over a mile and a furlong. There'll be plenty more to come from her."
Qemah is back again for Jean-Claude Rouget, having finished third in the race last year. She was arguably given too much to do when fourth in the Rothschild.
Harry Herbert, racing manager for owners Al Shaqab Racing, said: "She's a brilliant filly on her day.
"When she ran in this race last year we just felt she'd gone a little bit over the top by then. You could see in the parade ring beforehand she was a little bit anxious and her coat was going.
"This year's she's a bit more lightly raced and Jean-Claude is very happy with her going into it.
"If she could finish in the first three we'd be delighted and if she could win it, she'd stamp herself as a fairly brilliant filly."
Charlie Appleby's Wuheida was a Group One winner last season and has run respectably in two outings this season - without reaching the same level.
She was last seen finishing third in the German Oaks over a mile and three furlongs.
Appleby said: "She's in good order. She's come out of Germany well. That was her first time at that trip and she didn't stay, it was no more than that. She's coming back in trip. We're looking forward to that."
Last year's runner-up Persuasive also finished behind Roly Poly in France, but that was her first run of the year and she was not beaten far.
Chris Richardson, racing manager for owners Cheveley Park Stud, said: "It's a very tough race. Mr O'Brien is sending a lot of powerful guns into the fight.
"John (Gosden) is happy with our filly and I thought she ran very well in France.
"She was a bit unfortunate as she ended up the meat in the sandwich and didn't have a lot of room, but she ran on well when she did get in the clear.
"This has been her target. It might be a bit too tough - she's facing some serious opposition - but this is the sort of company she needs to be keeping."
Unforgetable Filly has won her last two races for Hugo Palmer but in nothing like the company she will face at Leopardstown.
"Her target is the Queen Elizabeth II Challenge Cup at Keeneland on October 14, so this is a sort of a prep run," said Palmer.
"If they get too much rain in Ireland, she'll run in the Sceptre (at Doncaster) next week."