My Pendant has risen through the grades with three straight wins during the late spring and early summer and she returns from a let-up in Saturday's Group Three Vanity (1400m) for three-year-old fillies.
“Her last couple of wins at Moonee Valley and Flemington were both very impressive and the obvious next step is to step up into stakes grade,” O'Brien said.
“She's had a nice little freshen up over summer and she seems to be in good shape so I'm looking forward to testing her against better horses on Saturday.
“I think she can hold that form from the summer and I'm obviously hoping that form is good enough to be competing against the fillies who were the best fillies in the spring.
“We'll all know a bit more about her on Saturday but it looks the right time to test her.”
O'Brien said My Pendant retained residual fitness having raced as recently as December 22 and the filly has also had a barrier trial at Cranbourne to have her fit enough for The Vanity.
Craig Williams has ridden My Pendant in three of her five starts for wins at Sandown, Moonee Valley and Flemington but he sticks with Amphitrite on Saturday who he won the Group One Thousand Guineas on last spring.
Amphitrite resumes for the Lindsay Park stable, after formerly being trained by the now-disqualified Darren Weir, and she was the early $3.70 favourite on Wednesday in a field of 11 while My Pendant, to be ridden by Damian Lane, was at $10.
Amphitrite easily won a jump-out at Flemington last Friday.
From barrier 10, O'Brien expects My Pendant to be ridden off the pace in her usual pattern before trying to utilise her turn of foot which the trainer believes is one of the filly's main assets.
“That's the exciting part about her, she relaxes very well in her races and she has the ability to really sprint at the finish,” he said.