Van Der Werf rode four winners from six rides at Omakau yesterday, her best tally since she began riding 11 months ago.
O'Cartier is the topweight with 59kg and Van Der Werf can claim 3kg.
"The last time he won was with a female rider. He seems to go well for them," John Parsons, the co-trainer of O'Cartier, said.
That was at Waikouaiti over 1250m on January 1 for the stable apprentice Tina Comignaghi, who was subsequently sidelined with a wrist injury. O'Cartier trounced his rivals including Coup Align, now in Singapore.
Trainer Daniel Champion said Shamrox would not start in the open sprint at Cromwell after a recurrence of a foot injury.
She missed the White Robe Lodge Handicap after casting a plate in the paddock and pricking a foot.
"The injury has flared up again and she won't race until Wingatui [next Saturday]," Champion said.
Fellini will also miss the race. Fellini was one of four winners yesterday for trainer Michael Pitman on his 56th birthday and the day after his 26th wedding anniversary. He is leading the trainers' premiership with 66 wins.
His apprentice Van Der Werf rode his other three winners - Peace, Coup Anabaa and Wine'nsoda.
The 17-year-old Van Der Werf has made the weekend for her parents, David and Karen. They have a wedding anniversary today and Karen has a birthday tomorrow.
Karen made the trip from Christchurch to Omakau.
She and her husband operate a property management business which has been hit by the earthquake.
"She [Courtney] had wanted to be a photo-journalist and we were not exactly thrilled when she took up riding," Karen said.
Courtney's uncle, Michael Wright, works for the Pitman stable and Courtney began riding work during the school holidays. She began race-riding 11 months ago at Riverton with a win aboard Kimberley Boy. She has ridden 14 winners.
David Dillon, a part-owner of Fellini, made the trip from Blenheim to see the gelding race.
Jim Campin, the Cambridge owner of Peace, was on the Otago Central Rail Trail.
• Lisa Allpress is making the trip from Wanganui to Cromwell, mainly to ride the Pitman-trained Eleanor Coup in the Cromwell Cup. She has ridden the mare to win at Waikouaiti and Ashburton this season.
• Shankar Muniandy outrode his 2kg claim when he won on Putri Delima yesterday. Muniandy, who is apprenticed to Brian and Shane Anderton, has ridden 60 winners.
Trainer Brian Anderton said he would decide overnight if he will continue with the engagement of Inferno in the Cromwell Cup. He said he was aiming Inferno at the South Island Breeders' Stakes (1600m) at Riccarton on March 26. His option is to give Inferno a lead-up race over 1400m at Wingatui next Saturday.
Shane Marr said Mt Difficulty would start tomorrow. The 3yr-old won decisively yesterday.
