For as long as she can remember, Marisa Goh has put pen to paper each time her older sister Theresa heads overseas, whether for training or for competition.

Sometimes it is just a short note of encouragement. Other times - like this latest instance for the Rio Paralympics - it came in the form of a little booklet, complete with illustration and messages from Marisa's colleagues.

Handed over at every airport send-off, no trip is complete without what the close-knit sisters call "last-minute letters".

For 15 years, this has been one of the ways in which Marisa, who is a year younger than 29-year-old Theresa, has shown support for a big sister she has only known to be "independent" and "strong". They have a younger brother, who is 25.

She penned her letter for Theresa's fourth straight Paralympics with more care than usual, mindful not to use words that may pin unnecessary pressure on the para-swimmer.

Marisa has seen for herself how crestfallen Theresa had been at the 2008 Beijing Games, where she finished fourth in the 100m breaststroke SB4 final and missed a medal by just 0.74sec.

"She's harder on herself than anybody else. We'll tell her it's okay, you've already made it to the world stage, but we know what she really wants is to be on the podium," she told The Straits Times yesterday.

After enduring a sleepless night, Marisa cheered and screamed - "as if (Theresa) can hear us" - when she streamed the race with her husband yesterday morning from her home in Hougang.

She also shed tears of joy, for she knows how much her sister had worked for and craved this medal - no matter how little she talked about it.

"I really didn't want her to think that everyone is expecting her to come back with a medal," Marisa, a creative visual merchandiser, said yesterday.

"We know what it was like at the previous Paralympics. We didn't want to see her heart break again."

Coming home empty-handed from Beijing in 2008 was the lowest Marisa had seen her older sister in an athletic career that has spanned 17 years, even if Theresa rarely lets it show.

"I guess in a way she felt like she let us down. She really tried to put up a very strong front," recalled Marisa. "She was on the verge of giving up but I'm so glad that she persevered. She really gave it her all, especially in recent years.

"Theresa's been the face of disability sports in Singapore and she's quite a natural at it. But I can only imagine the pressure she must have felt all these years.

"I've seen her train, but ultimately, I'm not in the pool, sweating with her. I know it's hard work but I don't think my perception is even close to explaining what it's like."

Happily for the Goh sisters, Theresa's hard work has finally paid off with her bronze in the 100m breaststroke SB4 race, with their parents Bernard and Rose having flown over to watch her swim in Rio.

"I really wish I could've been there with her and give her a hug. I know how happy my parents must be. We're just so proud of her," Marisa said.