England's Kildunne set to miss Women's Rugby World Cup quarter-final with head injury
The 2024 world player of the year was forced off early in the second half in Brighton after a worrying whiplash incident.
England finished top of Pool A by coming from behind early on against the Wallaroos to equal their own record of 30 successive Test wins.
Success, however, came at a cost with outstanding full-back Kildunne facing a mandatory minimum 12-day stand-down period after showing concussion symptoms, while powerhouse loosehead prop Hannah Botterman left the Amex Stadium field before half-time due to a back spasm.
Tournament hosts England face Scotland in the last eight a week on Sunday at Bristol's Ashton Gate.
"Ellie will go through return-to-play protocols," said England coach John Mitchell.
“There is normally a 12-day stand down. She is fine. She'll be frustrated because she had a difficult day at the office. She'll get better."
Mitchell, turning to Botterman, added: "Han's got a muscle spasm, so that will take its course.”
Sadia Kabeya and Kelsey Clifford scored two tries apiece after a converted try from Adiana Talakai stunned a crowd of over 30,000, including the Princess of Wales, by giving Australia a shock lead.
'Clunky' England
Jess Breach, Abbie Ward and Sarah Bern also scored tries in an ultimately convincing England win, with fly-half Zoe Harrison landing six of her seven conversion attempts.
"We didn't start well, we looked a little bit clunky, a bit untidy in attack, but I thought our defence was outstanding," said Mitchell, a former coach of his native New Zealand's men's All Blacks.
"Sometimes attack doesn't go for you, so it's something that was in our own control –- it wasn't something that Australia were doing to us."
England had already secured a place in the knockout phase thanks to thumping wins over the United States and Samoa, while Australia only needed to avoid an unlikely defeat of 76 points or more on Saturday to join them in the last eight.
The Wallaroos qualified as group runners-up –- ahead of the United States on points difference after their a thrilling 31-31 draw with the Eagles last week.
They will now face Canada, second in the world rankings, in the quarter-finals.
"The scoreline blew out a little bit in that second half," said Australia coach Joanne Yapp, a former England captain.
“The first half we were really in the game and were really competitive and we were executing what we wanted to do. But we always knew England were going to come out hard in the second half.
"Ultimately, we’ve got to the quarters, which was the first thing that we wanted, and there were areas of the game that were really positive."