Mary, 18, has enjoyed meteoric success since she started training with long-distance coach Chan Ka-ho at Tsuen Wan Athletic Club in November 2011.
First the former student at Li Po Chun United World College of Hong Kong won last February's junior women's half marathon at the Standard Chartered Hong Kong Marathon. This victory secured her a place in Hong Kong's junior athletics team.
Mary then started to take an interest in running the 3,000 metres steeplechase. Only two months later she won her first race in the event - in Round 2 of the Xtep Hong Kong Athletics League - in a time of 12 minutes 12.28 seconds - about 34 seconds faster than the Hong Kong junior record.
After that Mary couldn't stop winning, or breaking her own Hong Kong record in the event; she went on to beat her best time in four more races.
"I'd taken some sports training in Muay Thai, Parkour [obstacle jumping] and badminton before doing the steeplechase," she says. "Coach Chan thought I was a very active sportswoman and so asked me to run the steeplechase, but I had no idea what it was."
The women's 3,000 metres steeplechase event involves running seven and a half laps of the 400-metre track and jumping over 35 76.2 centimetre-high hurdles and also a 70 centimetre-deep water pit. It became an official Olympic athletics event at the 2008 Beijing Games.
"I'd only seen magazine photos of runners trying to clear the water jump before," says Mary, who is taking a gap year before starting university.
"After hearing my coach's explanation about the event, I started to realise that to excel at the event involves practising some very complex techniques.
"My first race was the only time I'd completed the full distance with all the barriers. I'd found it quite tiring while practising over two laps in training, but in the real race I found it more relaxing than I'd expected."
Mary broke her own record at the All-China Junior Championships in Changzhou , then in Round 3 of the Xtep Hong Kong Athletics League, again at the Asian Junior Championships in Sri Lanka and finally at the Thailand Open Track and Field Championship. Her record now stands at 11 minutes 29.11 seconds.
She says her natural love of sports has helped her compete in the steeplechase. "You need to be quite fit and pace yourself and have endurance," she says. "And it helps that I'm not afraid to jump the hurdles or the water jump."
Her success has attracted tremendous attention from media and the public, and also helped raised interest in the event.
This summer Mary heads to the United States to start her degree studies at Princeton University, where she also hopes to improve her steeplechase skills.
"The steeplechase event is very popular in the US, and the standard of athletes in university teams running in National Collegiate Athletic Association competitions is high," she says.
The world record for the women's 3,000 metres steeplechase is 8minutes and 58.81 seconds.
"Many university steeplechasers finish the race in only 10 minutes," says Mary. "I hope if I train with top athletes at Princeton I can improve my time even more."
Before she leaves, you can see Mary try to break more records in the halfmarathon at the Standard Chartered Hong Kong Marathon on February 23, and the 3,000 metres steeplechase in Race 2 of the Xtep Hong Kong Athletics League in April.