Winona Costin has had a tough final year of her apprenticeship.

Her quest for back-to-back Sydney premierships in the junior ranks was derailed by injuries which kept her out of the saddle for three months of the season.

Despite that, she returned from her latest injury to ride Rock On Zariz to victory in the Highway Handicap on June 25.

Costin took her season tally to 18 Sydney winners when Braces won at Warwick Farm on Wednesday.

The injury lay-offs have denied her a chance to outride her claim, which is 1.5 kilograms at metropolitan meetings as she prepares for rides in six of the nine races at Rosehill on Saturday.

But Costin, who is indentured to Peter and Paul Snowden, is keeping it simple as she prepares for her first senior season.

"Pete's been really good," Costin said.

"He lets me ride outside work at various different tracks rather than just staying at Randwick now that it's approaching the end of my apprenticeship."

The transition from star apprentice into the competitive world of Sydney's senior ranks has brought many before her undone.

But, Costin who is boosted by being able to ride at 50kg, is keeping it simple as she prepares to graduate.

"I'll just keep doing the same thing," Costin said.

She plans to continue riding work for the Snowdens at Randwick twice a week, as well as at Rosehill and Kembla Grange for other stables.

"I'll probably go down south and up the coast a bit to ride races as well," she said.

Costin will ride Slate On Edge in the 1200m benchmark 93 race at Rosehill on Saturday.

It will be the start of a familiar preparation for the Brett Thompson-trained gelding, starting his campaign in Sydney before travelling south to target Melbourne's greys races.

"He'll stay in the city because he's too good for the country," Costin said.

Costin said her win on Casino Dancer in the Group Three Angst Stakes as a $51 chance was the highlight of her apprenticeship.

She also has a special place in her heart for one of her favourite horses I Am Snippety who she rode to victory in the $100,000 Wellington Boot in March 2014.