"I don't really know what happened in Moscow," she explains. "I had breathing issues for more than half of the race and if I had not been representing New Zealand, I would have pulled out of the race. They later found a cyst on my spleen, but they were unsure it contributed to anything."
Following Moscow and with the long term ambition to make the marathon team for the Rio Olympics, she took a break from the sport and gave birth to her second child, Olivia, in July 2014.
Returning to training later that year and now under the guidance of Houston-based Rice University coach Jim Bevan - although she is still in regular contact with her long-time former coach and mentor Whangarei-based Ian Babe - she returned to competitive action in early 2015 and targeted April's London Marathon in an effort to attain the time for Rio.
Mary prepared well and was optimistic of a good outing, but just a week before the race she picked up a plantar fascia injury. She opted to run with the problem, but fell well short of the B qualification standard of 2:29:00 - running 2:34:22 for 17h.
Mary switched her focus to the Toronto Marathon in October, but was to suffer more last-minute heartache as just seven days out from race day a hamstring issue flared up. She took to the start line, but was forced to quit after 8km with a hamstring pull.
"I was devastated after Toronto," says Mary. "I had trained very hard for both marathons that year and to know how much work I had put in only to get injured so close to the marathon was tough to take."
With less than a year to go before Rio she did not see it as a realistic aim to qualify for the marathon. However, with a 10km road PB of 32:09 - six seconds under what she needed to get a B qualification for the 10,000m distance - Mary decided to return to track running after a ten-year break.
As a 2005 World University Games and 2006 NCAA Championship 10,000m bronze medallist she had some pedigree over the 25-lap distance and in preparation for her quest set about re-introducing more track and speed work into her programme.
After initially finding the move a "real shock to the legs" she set early season PB's for the 1500m and 5000m before targeting her first 10,000m in Norwalk, California in mid-April.
Mary set a PB by more than 18 seconds, recording 32:49.76 - but had "mixed feelings" about the performance.
"I thought I was capable of around 32:30 and although I was happy to get a track PB, I thought I was maybe fitter than I was at that point," she explains.
Two weeks later she returned for her second and most realistic crack at the Olympic qualification standard at the prestigious Payton Jordan Invitational in Stanford. She ran some 16 seconds quicker - posting 32:33.55 - than she did in Norwalk to place sixth in the B race, but ultimately failed to meet her qualification goal.
"I knew I had one more race in Portland to go, but that Stanford would be my best opportunity," explains Mary, who is married to Gabriel, a Brazilian. "I maybe should have pushed harder to be in the A race but I am not sure I would have found an extra 15 seconds or so which I would have needed (to reach the standard)."
On June 7 at her last chance saloon qualification opportunity in Portland she trimmed 2.33 from her lifetime best to record 32:31.32, but suffered for sitting behind a race pace which was simply too slow during the early part of the race.
"It was such a devastating thing to miss out because it had been such a goal for so long to compete at the Olympics," she says. "It was tough, but returning home to see my kids' happy faces put life in perspective."
Inspired by watching the Kiwi success at the 2016 Rio Olympic Games she has put her personal Olympic disappointment behind her and re-set her goals.
Training around 100 miles per week and returning to "longer efforts," which have served her so well in the past, she is hoping to use this weekend's B.A.A Half-Marathon as good preparation for her hometown marathon in Houston in January, where she hopes to target a qualification mark for the 2017 London World Championships.
Beyond that the 34-year-old mum-of-two will look to compete at the 2018 Gold Coast Commonwealth Games and she has certainly not given up on her Olympic ambitions with Tokyo 2020 in her sights.
"I was disappointed to miss out on Rio, but ultimately Tokyo is the goal," he says. "It will depend on how my body ages and how it holds up, because I will be 37 by then, but that will be the aim."
