The family of a Nova Scotia teen who died after collapsing while running the Toronto Marathon on Sunday believed she was being taken to hospital for dehydration.

Emma van Nostrand’s father, Steve van Nostrand, said his daughter’s cousin had seen Emma being taken to an ambulance but didn’t realize the urgency of the situation at the time.

"My wife caught up with (the cousin) just before she finished the race, so the two of them knew that Emma had needed help, but figured she was just dehydrated or something," van Nostrand told the Cape Breton Post.

Van Nostrand, along with his wife and daughter's cousin were also participating in the Goodlife Fitness Toronto Marathon when Emma had collapsed near the finish line.

The family said they tried locating the 18-year-old in the medical tent after the race but were told she had been taken to St. Joseph’s Health Centre where they learned of her death.

"Obviously, it’s very devastating for us because we expected to pick up our daughter after being dehydrated," said van Nostrand, adding that his daughter did not complain of any health issues prior to the race and that there was no known history of heart disease in the family.

He said Emma had completed three half marathons in the past 18 months.

Sunday's 42-kilometre race was supposed to be the teen's first full race.

Dr. Chris Milburn, a family friend of the van Nostrand's, said he thought there had been a mistake when he heard the news of Emma’s unexpected passing.

"I was sure it was mistake when I first heard it, and didn’t really believe it until I heard from a second source," Milburn told CTV Atlantic.

In addition to running, Emma also participated in a number of sports at her high school in Coxheath, N.S.

"She played soccer for us. She played basketball for us. She was an honour student," Riverview High School principal Joe Chisholm told CTV Atlantic.

Van Nostrand said the family is awaiting for a report from a Toronto coroner. He said the "best information" they have is that his daughter collapsed and she didn’t regain consciousness. "We don’t believe she suffered," he said. "It sounds like a situation that was predisposed and not necessarily cause by the marathon, but brought out by the marathon."

According to Milburn, runners dying from participating in long-distance races is rare. "This kind of event, that we call sudden cardiac death in athletes, can occur during any kind of athletic competition," he explained. "So it’s nothing to do specifically with stress of the marathon."

On Monday, a crisis intervention team visited Riverview High School.

Van Nostrand said his daughter had just returned to school this semester after spending three months overseas in France to improve her French.

"She lined that up on her own, she was very focused, driven person," he said. "About this time last year she came to her mother and I and said, 'I'm doing a French exchange to France three months next fall.'"

The Grade 12 honour student was planning to attend Dalhousie University in the fall where she was going to pursue a bachelor of science degree in psychology.

With files CTV Atlantic’s Ryan MacDonald and the Cape Breton Post