Sydney's champion apprentice elect – she has had the title sewn up for months – can do it in any manner. From last like she did on a brute of a two-year-old in the first at Rosehill on Saturday, where she threaded her way through the ruck, or running amok on speed on an older horse such as Beauty's Beast.

It is not hard to see why there is no more in-demand rider in Sydney this winter, regardless of the fact Costin will shed another half-kilogram from her claim after a 50th metropolitan win at Rosehill on Saturday.

"I was only just starting to ride city winners at the start of the season," Costin said after a first city treble. "It [the premiership] wasn't really a huge goal. I thought it would be hard to achieve, but now I'm here I'm stoked to be here. It's a season that's gone over and above my expectations. It's just been brilliant."

Godolphin's apprentice Brodie Loy is the next most successful junior on Sydney tracks this season, but 16 winners pale into comparison to Costin's tally of 39.

She will become just the second female to win the apprentice crown – and first since Kathy O'Hara 10 years ago – when the season winds down next month.

It hasn't all been plain sailing though. She had a rift with Gai Waterhouse, patched things up and then eventually left for Peter and Paul Snowden. Not that the 20-year-old seems bitter about it all.

"Mrs Waterhouse was fantastic to me earlier and Paul and Peter Snowden have been brilliant to me," Costin said. "I'm really enjoying my time with them and I'll keep chipping away. I still have about eight months or so [of my apprenticeship to go], but if I don't outride my claim I might extend [it]. Trying to outride my claim would be my next goal."

That might be a little harder now given she can only receive a 1.5kg allowance, but the work ethic won't stop as she drives down to Moruya for the Bateman's Bay Cup meeting on Sunday.

The wins on Intrepid Way, Queen Of Kariba and Beauty's Beast at Rosehill came for different trainers – but it still pales into the five-timer she chalked up at the Sapphire Coast in early 2014.

"To be able to come to a Saturday at Rosehill like today and have seven rides is brilliant ... and they're all for different trainers," she said. "It's only half-a-kilo [less of the claim] and I'm on a bit of a roll at the moment so as long as I keep rolling along [it should be fine]."

While it was all one-way traffic in the apprentice title race, there was little movement in the senior crown.

Both Hugh Bowman, on 83 wins, and Blake Shinn (81.5) went without success as James McDonald (88.5) maintains pole position.