Radhika Sharma's parents, Ramesh Sharma, 65 and Neelam Sharma, 64, two US citizens who live in New York City, were also travelling to Mount Kailash in the Kathmandu region when the disaster struck.
The pilgrimage was their first trip on their own since retiring last year.
"I am just trying to find them, I don't have any answers," Radhika Sharma told the BBC. Sharma is typically in frequent contact with her parents, often texting multiple times during the day.
"The last we know is they were at the border at 8 am, so about an hour before the floods," she said. "And we are hoping that they made it to the Tibet side."
Sharma, who has been in contact with the US embassies in in Beijing and Kathmandu, said: "No one has any answers."
She has also connected with other Americans who are in a similar situation, to support one another and consolidate information.
Prabhath Sajeepa is another US citizen who went missing after the flood hit. Sajeepa works for a software company in California, and was also on the sacred pilgrimage to Mount Kailash.
"It has been terrible. I hope he is somewhere safe," his niece, Kavya Koulagi Jayatheertha, told the BBC. "We are hoping for good news."
The US State Department said that the US embassy in Nepal was working closely with local tour agencies and authorities to assist affected Americans, a spokesperson said.
Officials did not provide figures or additional details regarding the Americans affected for privacy reasons.
Canada's foreign office said it was monitoring developments and was ready to provide assistance if needed.
Canada's Prime Minister Mark Carney said all Canadians in the region should sign up for Registration of Canadians Abroad, a free service that lets the federal government contact and assist citizens during an emergency in other countries.
The foreign office said 820 Canadians are registered as being in Nepal and five Canadians are registered as being in the Tibet Autonomous Region, China, citing the Registration of Canadians Abroad system.
"The Department is aware of Canadians who have been affected by the floods," the Global Affairs Office said in a statement to the BBC.
According to Nepal police, more than 500 tourists are missing from 28 different countries - most of whom are foreign nationals.
The Nepal Tourism Board has broken down the missing by nationalit, externaly.
State media in China, which controls Tibet, reported three dead and at least 558 missing there. Among these are 260 foreign nationals, CCTV said. It is not clear if these figures overlap with Nepal's.
CCTV from Tibet showed a wall of water and mud hitting buildings at a border crossing.