Sze, 25, is a full-time swimmer who specialises in butterfly and freestyle events. She has been training at the Hong Kong Sports Institute with retired Hong Kong team head coach Chan Yiu-hoi since she was in Primary Six.
She turned pro after finishing Form Seven at Diocesan Girls' School in 2008. She has had ups and downs since.
Up: Sze qualified for her first Olympics in Athens in 2004.
Down: Four years later, she missed out on her second Olympic appearance by coming just 0.22 seconds late in the qualifying rounds of a 100m race in Beijing.
Undaunted, she set her sights on international competitions. "My target was to do well at the 2009 East Asian Games [held in Hong Kong]," she recalls. "I didn't lose motivation after failing to qualify for the Olympics."
Last year she made it to the London Games in the women's 200m freestyle. She came 23rd in the event. But despite her Olympic moments, it's her memories of the East Asian Games in Hong Kong that she treasures most.
"I would say I most enjoyed competing at the EAG," Sze explains. "Swimming is an individual sport but the morale of the whole team pushed everyone to a higher standard. Many of us did very well in front of the home crowd. I was really happy."
Although she is a veteran of the sport, Sze says she still swims with "the enthusiasm of an 18-year-old".
"I know I haven't passed my peak yet," she insists. "I love swimming and I am still able to swim faster. So I won't set an exact time as to when I am going to retire. If my form allows, I would like to keep going."
Over the years Sze, an Asian Games medallist, has set a number of Hong Kong records. She has also earned the respect of her teammates. Some younger swimmers see her not only as an inspiration but as a close friend and guardian. They have jokingly nicknamed her "Mum" for "mothering" them. "I tell younger swimmers about their weaker points [in the pool]," she explains.
"We have no generation gap between us at training camps, but I do take care of them and ask them to go to bed early."
So she doesn't begrudge the "Mum" label.
"It is a common practice for swimmers on the team to nickname others as family members. We've even had 'grandparents'," Sze says. "So 'Mum' is actually not too bad."
As she enters a new Olympics cycle, she is training with a new coach, Martin Grabowski from Germany, after the retirement of head coach Chan at age 61 last month.
Grabowski coached the German national team for eight years before taking up the post in Hong Kong.
Grabowski believes Sze should still aim higher.
"She will be 28 by the next Olympics [in 2016] and I think she could do well. She still has room for improvement," the coach says.
Sze and her teammates are now in Arizona, in the United States, for three weeks of highland training before the Asian Indoor Games and the World Championships.
Even as she is eyeing the next Olympics, Sze, who is taking a five-year part-time bachelor course offered by Beijing Sport University and the Hong Kong Sports Institute, has set herself another target.
"I want to win a medal at the National Games," she says.
"One of my teachers from Beijing in the bachelor degree course wondered if anyone from Hong Kong has ever won a medal at the Games. Her doubts have motivated me to do well at this high-standard competition."
But that will have to wait. "I am not joining the Games this year, so hopefully I will achieve this target in 2017," Sze says.