She said she could not allow her son to take the blame for what was a political matter.
Thepthai Sennaphong, Prime Minister Abhisit Vejjajiva's personal spokesman, said Simarak had taken a number of irregular steps to help her son, having withdrawn a bail request and started preparing for a royal pardon before the court had even issued its verdict.
Former foreign minister Prasong Soonsiri said Simarak and the opposition Pheu Thai Party had used Sivarak's case to discredit the Thai government.
"It has been a set-up from the beginning. The man will eventually get a royal pardon as requested by [ex-prime minister] Thaksin Shinawatra," he said, "and then they would blame the government for lacking the ability to help a Thai national."
Sivarak was sentenced to seven years' imprisonment and fined 10 million riel (Bt83,000) for sharing information about Thaksin's flight plan. He admitted to the court that he had given such information to a Thai diplomat, Kamrob Palawatwichai, who was expelled from Cambodia.
Rather than relying on assistance from the Foreign Ministry, Simarak asked Thaksin and the Pheu Thai Party to help in the process of seeking a royal pardon from the Cambodian king to free her son.
The Foreign Ministry is not in a position to help as it is in conflict with Cambodia, she said.
"I think the Foreign Ministry should stop providing any assistance to my family, since it could make things more complicated," she said.
"Former prime minister Thaksin and PheuThai Party chairman Chavalit Yongchaiyudh will be able to help us because they have better relations with Cambodia than the Foreign Ministry", she added.
"Please don't fear losing face as the real loser is my son. He has lost everything - his reputation and his job," she said.
"I beg understanding from those who think this is a set-up. That is a very bad attitude. No mother could take her son into such a risky situation. Our family would get nothing from this incident. Do you think any mother is happy to see her son in jail?"
It is hurtful to hear some government officials saying Sivarak is a troublemaker, she said. "It is diplomat Kamrob who caused trouble for my son. He made a phone call and said a few sentences asking about the flight, but my son has been jailed for seven years," she said.
Foreign Ministry deputy spokesman Thani Thongpakdi defended Kamrob, saying that the diplomat had been performing his foreign-service duty and did not need to take any responsibility for Sivarak's fate.
Pheu Thai Party spokesman Prompong Nopparit said Chavalit would sign a pardon request and send it to Cambodia's king via Prime Minister Hun Sen either late this week or early next.
The request will be forwarded along with the one prepared by a Cambodian lawyer for Simarak.