Her absence was considered a missed doping test, the first strike for one of Canada's top track and field athletes.
Three strikes is an anti-doping violation, and can come with a suspension of up to two years.
Some athletes are quietly complaining that they've become slaves to what they call a draconian anti-doping system desperate to keep up with the cheaters, saying they have to sign away their dignity and privacy to prove they're clean.
Few are keen to talk openly about it.
"It's really a system that's flawed on so many levels," says Zelinka's husband Nathaniel Miller, an Olympian in water polo. "It has nothing to do with athletes trying to avoid testing, but everything to do with athletes trying to just be normal human beings and have their own dignity and freedom respected.
"I don't think the current system does that."
Canada's top athletes must provide a schedule of their daily whereabouts in three-month blocks to the country's doping watchdog, the Canadian Centre for Ethics in Sport.
In the days following her bronze medal run at the 2008 Beijing Olympics, hurdler Priscilla Lopes-Schliep and husband Bronsen Schliep took a road trip to the Grand Canyon. They pitched a tent in a national park. Lopes-Schliep emailed the longitude and latitude of the campsite to her manager Kris Mychasiw, in case the drug testers needed to find her.
"The longitude and latitude, that's hardcore to expect an athlete to do that," Mychasiw said. "Thank God for smart phones. She sent the update in: 'We're in a tent, somewhere along the road, and here's the longitude and latitude.'"
Athletes are also required to designate a specific hour each day — any time between 5 a.m. and 11 p.m. — when they're available for unannounced drug testing in their home.
"If you're a regular employee in Canada, this entire policy and procedure is illegal," Miller says. "You're not allowed to do random testing in a person's place of living, they can't send a drug tester to your house to test you for privacy reasons. And yet, because you represent your country as an athlete, those rights go out the window."
Athletes must notify the CCES of any scheduling changes. Zelinka forgot to do that. She argued she was caught up in the stresses of a move to Connecticut, last-minute plans to participate in the Olympic parade in Toronto, and the added demands on her schedule that come with being a mom.
Zelinka, whose daughter Anika is three, appealed the missed-test ruling. Her appeal was recently denied. Two more strikes in 18 months will be an anti-doping violation.
"It's not like you're trying to hide something or trying to throw them off, which of course was absurd because she was at a very public celebration of Olympic sports," Miller said. "Her actual whereabouts were well-known to everybody, and anyone."
The CCES was formed in the fallout from the 1988 Ben Johnson scandal. Jeremy Luke, director of the Canadian anti-doping program, says the organization is complying with the World Anti-Doping Code.
"That code outlines the length of sanctions that can be imposed on athletes, the testing protocols, and then included in that, is what we call 'athletes whereabouts requirements,' which is an international standard that's implemented in Canada but also implemented around the world in other countries," said Luke.
Athletes unhappy with the testing protocol know their point of view might not be a popular one, especially coming on the heels of revelations of widespread doping in cycling, and the downfall of Lance Armstrong.
"You're kind of stuck between a rock and a hard place because if you speak out loudly against it, the immediate perception is: oh well, they're trying to hide something," Miller said. "Canadian athletes for the most part are strong advocates for drug-free sport, so you don't want to be criticizing an agency that you support — even though you don't support their methods."
Andreanne Morin, a rower and a member of WADA's athletes council, said Armstrong is the best argument for unannounced testing at home.
"It's not because (anti-doing officials) want to be complicated, or they want to be annoying," she said.
Morin, a member of the women's eight that won silver at the London Olympics, referred to the 202-page report on Armstrong's doping investigation, and evidence that the fallen U.S. cycling star used the blood-boosting hormone EPO.
"These guys would do EPO at night, and it's only detectable in your first urine sample in the morning. They would literally go into their hotel rooms, lock the door, and not answer it to absolutely anyone until they'd done their first urine in the morning," Morin said.
Many athletes complain the testing is excessive. Mychasiw said Lopes-Schliep and teammates Nikkita Holder and Phylicia George were tested more than 50 times last season between them.
Miller noted that the 31-year-old Zelinka was tested four times in the span of six days at the Olympic trials last summer in Calgary — the day before the trials started, the day of each of her victories in the heptathlon and hurdles, and blood tests the day after the meet.
"That is not just overkill, it's a huge waste of funding that makes no sense," he said.
A test costs between $500 and $800.
What bothers the heptathlete and her husband most is the unannounced testing in their home.
Protocol demands that from the moment an athlete answers the door, they're not allowed out of the tester's sight.
"So you're in your pyjamas, they have to come with you into your bedroom if you want to get changed, you have to get changed in front of them, you have no privacy," Miller says. "Then with women's monthly cycles, if you're caught in the middle of your monthly cycle and there's the desire to freshen up, you don't have that right, you have to do that in front of this complete stranger in your home in your bathroom — what is supposed to be your private domain."
Collecting a sample requires a doping control officer watching an athlete urinate into a bottle.
Some officers demand athletes "drop their pants to their knees and pull their shirts up to their chests," said sprinter Justyn Warner. Others are slightly more discreet, and "will watch over my shoulder."
Warner found it tricky to provide his whereabouts to the CCES in the months leading up to his recent marriage to Holder, a hurdler.
"We were kind of at both places, so she would be at my house, I would be at her house, and it made it hard to kind of pick that hour when you always had to be home," said Warner, who anchored Canada's 4x100-metre relay team that crossed third at the London Olympics but was then disqualified for a lane violation.
Warner said there were plenty of mornings of rushing home before sunrise.
"It's just the way they go about it, something needs to change in that aspect," Warner said. "But I don't complain about it. I wouldn't care if I got drug tested every week just to show people that I'm a clean athlete."
Holder once received a strike for a missed filing because she didn't properly click "submit" on the CCES online form athletes use to report their whereabouts.
"It's incredibly onerous and doesn't work on all devices," said Miller, pointing out that Zelinka has been using a computer at a local library since their move to Connecticut because the program doesn't work on her iPad.
The CCES website has a video tutorial on using the program, and once offered prizes such as gift certificates as incentives for athletes to submit their forms quickly.
Morin said there have been suggestions of tracking athletes by GPS.
"But I think that's even more invasive than what currently exists," Morin said.
Three-time world boxing champion Mary Spencer said unannounced testing might be intrusive but it's necessary.
She's has had postpone plans to produce a sample, including one Saturday night she was on her way out with her roommates. She made a pit stop in the upstairs bathroom, and didn't hear the knock of doping control officers at her front door.
"They all screamed up the stairs at the same time 'Don't pee!' because they heard the bathroom door shut and the drug testers had shown up. I'm like 'What the heck? Is there something wrong with the plumbing?'" Spencer said laughing.
"Seriously, this is what I think: If one of my competitors was doping, I would want them to do everything they could to catch a cheater. So for that reason, I am willing to break up a Friday or Saturday to accommodate them."
There are about 400 elite athletes in the Canada's registered drug testing pool, according to Luke.
In the quarterly period between July and September of 2012, there were 1,321 urine tests conducted as part of the Canadian Anti-Doping Program, plus 208 blood tests. There were two anti-doping violations in that time — one for testosterone and one for marijuana.
Athletes complain that testing protocol isn't as strictly enforced in other countries as it is here.
At the London Olympics, Canada's former WADA chief Dick Pound pointed to Jamaica and Belarus as two countries where tests are not rigorous enough, saying it's often difficult to track down athletes to test them.
Catriona Le May Doan estimates she's been tested "thousands" of times, and jokes about it now. But the two-time Olympic speedskating champion believes there's no alternative when it comes to keeping sport clean.
"It makes me adaptable to pee anywhere," she said. "If I ever get stuck in my car, I have no problem. I can pee in a cup."
"People say, 'Oh the system is skewed,'" she added. "But for athletes who are in the system, you have to trust it. Because that's all you have. It's always been a situation where you do it because you want to be part of it. You want people to trust you and you want to trust others."