Jim Cassidy has a couple of theories on why Dear Demi turned in the worst performance of her career in the Coolmore Classic.

More importantly, the in-form jockey can find several reasons why she can reassert herself as one of the nation's best fillies in the Group One Vinery Stud Stakes (2000m) at Rosehill on Saturday.

"On face value she was a bit disappointing last start," Cassidy said.

"But she got back and out of her comfort zone and it was hard for horses to make up ground."

Dear Demi finished 11th of the 14 Coolmore Classic runners, beaten almost five lengths.

It was only the second time in her 18-start career that she had finished further back than fourth.

Before that uncharacteristic effort, she had resumed with a slashing third in the Light Fingers Stakes and posted a dashing victory in the Surround.

Those performances were against her own age and sex, conditions she returns to on Saturday after taking on the older mares last start over 1500m.

Cassidy firmly believes she will bounce back.

"I do, back to three-year-old fillies grade and up to the 2000 metres," he said.

"She pulled up really well, nothing was amiss with her apart from the fact she just got out of her comfort zone."

The winner of the VRC Oaks in the spring, Dear Demi is equal favourite for the Australian Oaks.

A win on Saturday would almost certainly elevate her to outright pick.

Her major rivals in the Vinery include the Bart Cummings-trained Norzita who finished third in the Coolmore Classic but will need to pass her first test beyond 1600 metres.

TAB fixed odds has Norzita the $2.80 favourite ahead of Dear Demi ($4.60) and Habibi ($5) who was a last-start winner of the New Zealand Derby.

That trio are the clear top picks with Victorian You're So Good next best at $13.