Kelly finished runner-up in the 200-metre under 17 final at Sydney Olympic Park on Saturday, backing up her second-place result in the 100m final on Wednesday night.

Kelly, 15, said she was overwhelmed with the result after missing a medal in the 200m distance last year.

She crossed the line in a career-best 24.93 seconds behind Western Australia's Olivia Dodds (24.19).

"It was super exciting and I was pretty shocked because my main goal was to not finish fourth," she said.

The Emmanuel College student said she had worked hard to improve in the longer distance and was pleased to see a result.

"I think the last 50 or 100m of the 200m I used to struggle with," she said.

"My stamina wasn't as good towards the end of the race and girls would roll over the top whereas this past 12 months I've really been working on more longer reps and trying to make the last part of the 200m as strong as my first."

Kelly, who is part of the Duynhoven Perry Sprinting stable, also collected a bronze medal in the under 17 4x100m relay on Sunday.

"I was super stoked with how nationals turned out," she said.

"It wasn't the season I planned on, I had injuries leading up to state and nationals, so it wasn't the best preparation but it was the most successful nationals I've had so I was super rapt with how I ran."

Kelly will now aim for the Stawell Gift - a prestigious handicap race - at Easter.

She made the women's final last year, aged just 14.

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