The tiny Southeast Asian country, nestled on the north coast of Borneo in the South China Sea, had said in March they wanted to send Mahusin to the Games and break away from a trio of countries yet to take a female athlete to an Olympics.
However, with Mahusin's personal best clocked at more than 10 seconds outside the global athletics governing body's 'A' standard qualifying time, she endured an agonising wait to see if the IAAF would grant her an invite to compete.
Last week the news came through... she was heading to London.
"I feel deeply honoured, it's a dream come true, even though it's under the concept of universality. I am happy to see the flag of Brunei Darussalam being hoisted in London," Mahusin told Reuters in an interview.
"I was very nervous and at the same time anxious to find out who will be the first female athlete to represent Brunei. I'm even more nervous now because the Olympics are less than 21 days away."
Zuraimi Abdul Sani, secretary general of the Brunei Olympic Council (BOC), told Reuters by telephone that they planned to have Mahusin carry the country's flag at the opening ceremony in London on July 27.
"Of course we are proud," Sani said. "The members of the public are happy to hear that Brunei is taking part in the Olympic Games, especially with the sending of a woman to represent the country."
Mahusin's inclusion in the three-person team leaves Saudi Arabia as the only country yet to send a female athlete to the Games or committed to sending one to London.
Gulf neighbours Qatar will take three female athletes to London, the first time they will have competitors of both sexes at the Olympics.
While the two Gulf nations had resisted because of their ultra-conservative approach towards women in sport, Sani was keen to stress that Brunei had been unfairly labelled.
"As far as we are concerned, women are free to take part in all the events they want to take part in. We have no restrictions on women taking part in sports in Brunei.
"The interest in other women to be like her will definitely be there."
Brunei's four previous male Olympians did not win a medal and the team were expelled a day before the 2008 Beijing Games after they failed to register their athletes.
So the country's joy at sending a record amount of athletes to London is obvious, but the dream remains that in future one qualifies through merit.
Mahusin, 400 metre runner Ak Hafiy Tajuddin Pg Rositi and Anderson Lim Chee Wei, who will be Brunei's first swimmer to compete at an Olympics, are all participating on invites with personal bests in first round exits the aim.
Mahusin rejects the notion that all Olympians should qualify.
"I think it is very important for the Olympics to extend the opportunities to participate to smaller nations, as it forces countries such as Brunei to boost its level of commitment in developing aspiring athletes (especially female ones) so that they are able to compete at an international level," she added.
While Mahusin was keen to praise the BOC for their help in getting her to London, she acknowledged this was just the start.
"This should also serve as an encouragement for Brunei to aspire to a higher standard in sports and athletics.
"It is my aspiration to see more young women athletes participate in sport, I think women in Brunei should not give up too easily, and one must have a lot of patience and constantly motivate oneself towards self-improvement.
"The support for women to pursue an interest in sport is also desperately needed."