A competitive swimmer and gymnast, Mortimer raced in the 2008 Olympic swim trials and was hopeful of making the Canadian team for London.
Just a few months later, on Nov. 28, she bounced off a trampoline and missed the sponge pit. Mortimer landed on the corner of a cement pad and shattered virtually all the bones in her feet.
She was in a wheelchair for a year and a half, followed by another year and a half on crutches. After two surgeries on her left foot and one on her right, the prognosis wasn't good.
"They didn't think I would keep my feet," she recalls. "They were considering amputating both of them. When they said I could keep them, they said I'd never walk again."
"As soon as I was out of the wheelchair, I was teaching myself to walk again as well as swim."
Mortimer will compete in London, but with Canada's Paralympic swim team. She holds world records in the 50-metre freestyle, 50 backstroke, 100 backstroke and 200 backstroke.
She races in an S10 classification, which is defined as minimal physical impairment. Mortimer has six screws and a medal plate in her left foot, which is clubbed, and another two pins in her right foot.
The 19-year-old from Newmarket, Ont., had a unique vantage point at this year's trials in Montreal, where both Olympic and Paralympic swimmers were racing for the right to go to London.
Having participated in the able-bodied side of the sport just four years ago, Mortimer is adjusting to life as a Paralympian.
"Looking at it and thinking 'I could have been with them' and now I'm on the Para side, it's not bad, but it's a very big change," she says. "Going from being an able-bodied athlete to a Para-athlete, I know the amount of respect and credit is completely lacking in the Para side.
"I know truckloads of able-bodied athletes who constantly make fun of the Paralympics and say it's a joke. It's not a joke. I've learned first-hand."
She's optimistic for Paralympic sport though. Swim teammate and multiple medallist Benoit Huot has told her how much attitudes have changed since his first Paralympics in 2000.
"He says from 2000 to 2012, it's a huge difference," Mortimer explains. "Especially with this generation, everyone is more accepting. You look at sexual orientation, you look at religions, you look at culture, everything is about being individual and having equality and freedom.
"I think the Paralympics are going to skyrocket, especially for 2016. I think that's where you'll see it especially. London is certainly a big deal, but I think in another four years, that's where you'll start to see more people getting involved."
The London Paralympics start Wednesday and run through Sept. 9.
Mortimer's 100 world backstroke record is one minute 6.47 seconds. The Canadian record on the able-bodied side is Sinead Russell's 59.68.
Mortimer says she considered racing against Russell at trials, but knew her best chance of going to London was in Paralympic swimming.
She's a threat to win multiple medals in London if her feet co-operate. The plates and screws cause her bones to suddenly lock up. That and accompanying tendinitis in her legs wreak havoc on her training, she says.
"My coach will say 'OK we're doing sprints training' and my feet will give out after 20 minutes of practice," Mortimer explains. "Once they lock up, I'm stuck in that position for awhile. Who's to say if it's an hour or the rest of the day?
"Everything is up in the air with training. I always deal with pain. It's just when it's the least and how much I can handle.
"It's degenerative so it will get worse with time. They didn't think I'd walk or keep my feet so I'll probably prove them wrong for as long as I can."
It's a wonder Mortimer walks across the pool deck with halfway normal gait. She refuses to hobble, even when people think she should.
"After the first competition I had, the world championships, I came back and (had) all these anonymous e-mails," Mortimer recalls. "The first one I got was 'How do you feel about walking in and taking medals from people when you forget to fake your limp 50 per cent of the time?'
"I don't think I look disabled. I hide it really well. Because I don't show pain, I get a lot of criticism. I'm sorry. I'm stubborn as a mule. I've been through too much to show any sign of weakness."
Mortimer likes to paint murals when she's not in the pool. She illustrated a children's book written by her twin sister Julia titled "The Night I Met The Boogie Man."
Meanwhile, she's gearing up for her first major Games.
"Just trying to picture being overwhelmed by it is how I prepare for it," Mortimer says. "I don't think you can avoid it. I think it's being ready to be overwhelmed and embracing it."