They are purposeful lapses, what she describes as her "cheat days", when her coaches allow the mixed martial arts (MMA) fighter to ease down the intensity of her workouts, indulge a little in her favourite greasy food and drink and, most importantly, rest her mind. A "cheat day" lasts 24 hours.
Three weeks into her training camp, with her calves and thighs groaning loudly under the strain, and her knuckles, shoulders, hips and back complaining of pain, she strayed on a couple of occasions.
Mostly, the Singapore fighter has had to be religious in focus and discipline, a disciple of tough workouts, plain eating and plain drinking while turning in early every night, fuelling her "crummy mood" she told me recently, as she worked to make the weight and be ready for her debut in the ONE Championship cage in Kuala Lumpur tomorrow night against Malaysia's Ann Osman.
It has been a world of intense drills these last seven weeks for Ooi, a time of metronomic boxing lefts and rights, seemingly endless jiu-jitsu moves and wrestling hooks and submissions practised, screams and shouts of anger and hurt accompanying every muay thai kick.
Ooi is 41, and hers is a remarkable tale of early promise in the swimming pool, competition at the SEA Games and Olympics, lengthy stays in faraway climes, medical studies, a life-changing decision, love gained and lost in tragic circumstances and now tomorrow.
When she has a chance to set the tone for Team Singapore at the SEA Games with a win over the Malaysian champion in a strawweight fight at Stadium Negara.
I've met Ooi often these last few months.She's a woman of poise, muscle and energy, engaging, generous, funny and easy-going, and she loves sport, any sport. Ooi the pugilist only ever talks of a win but we know fighters only read from this well-worn script before a contest, as if it can magically summon even more self-belief.
She could lose tomorrow night, under the pressure of the occasion against a motivated champion drawing strength from a home crowd that will generate that loud wall of sound synonymous with the famous old arena when it used to host badminton events.
Over the years, the home support at Stadium Negara has made visiting world and Olympic badminton champions wilt, what more ONE rookie Ooi, who will have butterflies in her stomach as she makes her debut under the intense lights of Asia's biggest MMA banner.
But, because of her discipline and focus, she can also block out all distractions, apply what she has learnt and come through. It has been part of her make-up since she started swimming as a six-year-old.
She was 13 when she first swam for Singapore at the 1989 SEA Games in KL and the freestyle and butterfly ace won four gold medals - 200m fly, 400m individual medley, 4x100m free relay and 4x100m IM relay - and collected a host of silvers and bronzes by the time she retired after the 1997 Games.
She swam in six individual events at the Barcelona Olympics in 1992, graduated premed from the University of Nevada and then earned a medical degree at Charles University. It is a list of accomplishments that would make many of us envious, and Ooi, still in her early 20s, had a career in medicine beckoning.
But she felt sport was her calling and never looked back once she decided it was martial arts over medicine.
She has been training in martial arts for nearly 10 years. She owns a gym where she teaches the Brazilian discipline capoeira and started fighting competitively only three years ago.
In her speech as chairman of the organising committee for the inaugural Chiam See Tong Sports Foundation Gala Dinner last Saturday, she turned storyteller, describing how sport had inspired her and infused her with a can-do spirit which she hopes to instil in youngsters.
It was eloquent and stirring.
She wants to help the fight against obesity, while continuing her MMA career. First, Ooi can breathe fire into Singapore's athletes as they get set to make this the country's most successful away performance at the SEA Games. She enters the cage tomorrow with the memory of her fiance and coach very much in her mind and heart.
He died last December in a motorcycle accident in Bali. She has managed to compartmentalise her grief magnificently, but will look to draw strength from his memory against Ann. Sport has worked its wonderful powers on Ooi, even if she does cheat on occasion.
This article was first published on The New Paper, Aug 17, 2017.