Disability support worker and mother of twin daughters Renee Spry was making a pilgrimage with the Isha Foundation when the deadly inundation hit on Wednesday morning.
Her last known location was at an immigration office along the Nepal-Tibet border, the destruction of which was captured in widely shared footage.
Describing her sister as a deeply spiritual person, Clair Spry told AAP that Renee had been planning and looking forward to her journey to the pilgrimage site of Mount Kailash for a long time.
"Our family's pretty realistic about what this is … everyone's got that little slither of hope that she is just stuck somewhere and helping and she can't get to us," Ms Spry said.
"But then also, we're very realistic, she was in the immigration centre 10 minutes before the wave hit."
Ms Spry added her sister would hate being the centre of attention and it would be important to her that people keep in mind the locals who had been displaced.
The family has established a GoFundMe page to support Renee's partner Shaun and twin daughters and eventually facilitate their travel to Nepal, but they have also asked people to give money to Save the Children's relief efforts.
The Australian government has confirmed that 42 citizens are among the nearly 3000 people still unaccounted for after flash flooding struck.
"We haven't given up hope," assistant minister Matt Thistlethwaite said on Sunday.
He highlighted the example of formerly missing Sydney woman Cara Severino, who made contact with her parents on Saturday and was safely located by Australian consular officials on the same day.
In a statement, Ms Severino's parents Debbie and Frank said they couldn't wait to "hold her in our loving arms".
"Seeing Cara's name appear on (our) message bank, hearing her voice and now seeing her photo and speaking with her has been the most miraculous gift," they said.
The Severinos thanked consular workers for bringing her to safety and her Nepalese hiking partners, who also made it to safety.
Prime Minister Anthony Albanese opened his remarks at Sunday's Queensland Labor conference with a moment of reflection for those caught up in the tragedy.
"That something so devastating could occur in such an awesome and inspiring corner of the world during times of pilgrimage and holiday makes the blow seem even more heartbreaking," he said.
NSW mother-of-two Reshma Patel was travelling in the same group as Renee Spry when the wave struck the immigration centre.
Also on the tour was outdoor education leader Michael Keats, and mother Sumi Adhikari.
Nava Pandey, who flew to Nepal following the disaster to seek out information about Ms Adhikari's whereabouts, said he still had no clear information about the status of his wife or the other members of her group.
"Families should not be left without answers during such a critical time," he said.
"Every hour matters."
Jen Nai said her family was desperately waiting for news of her brother-in-law Karan Bhardwaj, who was travelling with friends Arpan Mithalal Kothari and Bhavin Raval as part of a tour group with Kailash Journeys.
Other Australians missing include 15 people who were on a trek with US travel company Himalayan Glacier Adventures, including two boys aged 11 and 14 and a Sydney couple with two sons in their 20s, both studying medicine.
Rescuers have worked around the clock since a glacier collapse unleashed a huge torrent of rock, ice, mud and debris on Himalayan communities.
Nearly 700 people have been confirmed dead following the tragedy, but the toll is expected to rise rapidly as more bodies are uncovered.
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