But oldest-of-five Ruan credits the epic battles with her siblings – including future NRL forwards Tariq, Ashton and Korbin – for the competitive spirit that sparked her remarkable rugby league career.

Sims, 35, added to her already impressive resume when named Jillaroos co-captain for the women's Rugby League World Cup on Wednesday along with retiring duo Steph Hancock and Renae Kunst.

Australia face a mighty challenge trying to defend their crown in the six-team tournament starting on November 16 in Cronulla, with three-time cup winners New Zealand, traditional powerhouse England and dark horses Canada standing in their way.

But it is nothing compared to what Sims stared down growing up.

The self-confessed league nut thought it was a good idea to organise backyard contests with her three brothers and sister Canecia.

Then her brothers starting growing. And growing.

Ashton is now a 193-centimetre, 111-kilogram forward playing in the English Super League.

Korbin turns out for the Brisbane Broncos, stands 189cm and tips the scales at 108kg, while Tariq is 193cm and 105kg and is at St George Illawarra.

Still, Sims reckons she won a few one-on-one battles with the hulking trio before deciding discretion was the better part of valour.

"My parents were great building that healthy rivalry between us with those backyard games," Sims said.

"That really helped give us that drive to be where we are today.

"And you'd be surprised at how many family arguments can be decided by a backyard game of footy."

So how did she fare against the boys?

"If all five of us were playing it would be Ashton and I against the other three but sometimes the other three didn't want to play, so it was just Ashton against me," Sims said.

"It was pretty even. Then the boys started getting bigger, so I sort of took a step to the side a bit and watched them fight it out."

All three brothers have also gone on to play for Fiji, thanks to their mother Jacqueline's heritage.

And Sims believes Canecia will soon join her in the Jillaroos side, ensuring all five children have played international rugby league.

Canecia has already represented Australia in American football and was recently named in the south-east Queensland development squad after just four months in league.

"Hopefully I am still around but it would be pretty amazing running out with your sister playing for your country," Sims said.

The Jillaroos open their title defence next Thursday against the Cook Islands in a triple-header.

The final will be held on December 2 in Brisbane as a curtain-raiser for the men's World Cup decider.