But arguably the real setback was to come for the former world champion - failing to qualify for the national team in her pet event 100m freestyle.

Rather than leave the 25-year-old dispirited, Campbell says her troubled trials experience had only spurred her on to recapture her greatness at the 2020 Tokyo Olympics.

Campbell took the first step when she bounced back from her 100m disappointment to seal an individual nod for next month's world titles in South Korea in the 50m freestyle.

Campbell dug deep to clock 24.17 seconds and finish second just 0.12 behind her sister Cate in the 50m final on the final night of the six-day trials on Friday.

It almost made up for missing out on a 100m freestyle berth on Thursday night - almost.

Campbell admitted it was bittersweet after finishing within the qualifying time in the 100m final but ultimately missing out because she finished third.

The top two in each final earn world titles qualification providing they also finish under the nominated qualifying time.

Remarkably the top four finishers in the 100m final touched the wall within the qualifying time of 53.20 seconds - winner Cate Campbell, Emma McKeon, Bronte Campbell and young gun Shayna Jack.

"I have had that (100m) individual spot for six years in a row so that was a big one for me (to miss out)," Bronte Campbell said.

"To go under 53 seconds and not get an individual spot, that's incredible.

"It was bittersweet but I have the hunger to get that individual 100m spot back again."

Campbell stepped out of her famous sister Cate's shadow when she claimed the 50m-100m freestyle double at the 2015 world titles.

However, injuries including her lingering shoulder issue that required surgery in 2018, conspired to ensure she had never re-scaled those heights.

Then illness derailed her world titles preparation.

Yet Campbell was confident that she could regain her mojo ahead of Tokyo after defying her troubled preparation and 100m disappointment with a fighting 50m freestyle effort.

"I am so happy with that. It means a lot. It's been a very disrupted preparation," she said.

Her sister, Cate Campbell, tipped her sibling to bounce back in the 100m at Tokyo after revealing the full extent of the ex-dual world champ's nightmare trials build-up.

"She has been battling illness the last six weeks," she said.

"Her results are a testament to her courage, determination and self belief - she is only going to come back bigger and better."

Australian Associated Press