"I advised her not to listen to outside noise or pay too much attention to what others say," Lee Wu-nan said ahead of Lin's semi-final on Wednesday, which she went on to win.
"Many people previously questioned her gender but I said those were just psychological tactics meant to disrupt her.
"I told Lin not to be afraid; all of Taiwan supports you, including former President Tsai Ing-wen, who came to watch her practice."
The 28-year-old Lin moved a step closer to Olympic gold when she beat Turkey's Esra Yildiz by unanimous decision in the women's featherweight semi-finals.
Lin and Algerian boxer Khelif, a silver medallist at the 2022 world championships, have been in the spotlight at the Paris Games as part of a storm that has dominated headlines and been much discussed on social media platforms.
Both boxers were disqualified by the International Boxing Association (IBA) from the 2023 World Championships in New Delhi, with the body saying in a press conference on Monday that a sex chromosome test had ruled them ineligible.
They are competing in the Olympics after the International Olympic Committee (IOC) stripped the IBA of its status as the sport's governing body in 2023 and took control of organising the boxing in Paris.
"The gender issue is nonsense - she has always been female," said Lee.
"She has been tested many times throughout competitions, and once they even took her to Chang Gung Memorial Hospital for a check-up, and there were absolutely no issues. It's nonsense."
The IOC has rejected the results of the IBA-ordered tests as arbitrary and illegitimate, saying there was no reason to conduct them.
IOC president Thomas Bach has also said that there was no doubt that the two boxers were women.
The Philippines' Nesthy Petecio, who fights in the same division as Lin, said the Taiwanese boxer was a tough opponent who deserved to make it to the final of the competition.
"She's one of the very tough contenders here in the Olympics, so I thought that we will see each other in the final," Petecio said after her defeat to Poland's Julia Szeremeta in Wednesday's other semi-final.
"She's a good boxer, a strong one, a talented boxer. I've fought her twice already, and I know the capacity of Yu-ting.
"I don't have any comments regarding that (controversy) but all I know is Yu-ting and the Algerian boxer, they were born female."
Lin faces Szeremeta in the final on Saturday.
