She wasn't even allowed to use the restroom alone, she said of the April arrest.
"They made this woman go into the bathroom with me to watch me," she said, adding that the woman even entered the shower with her. "She even handed me the towel."
"I think they wanted to humiliate us ... to intimidate and humiliate us," she said.
It was her husband's second arrest accusing him of committing financial crimes while serving as Nissan's CEO. He's denied all accusations. Carole Ghosn said her husband, who's spent at least 130 days in detention in a Japanese prison since November, was interrogated for eight hours every day without a lawyer.
Carole Ghosn is complaining publicly about what she characterized as "inhumane and cruel" treatment of the couple ahead of Japan's first G-20 summit, which is being held in Osaka at the end of the month.
Carlos Ghosn was first arrested last November in Tokyo, facing allegations that he diverted Nissan funds to a Saudi businessman and friend, underreported his compensation, and engaged in a breach of trust tied to personal trading losses.
Ghosn stepped down as CEO of the Japanese carmaker in 2017. His trial on financial misconduct charges was expected to begin in September, but will be delayed.
Carole Ghosn said she's hoping foreign leaders pressure Japanese officials to ensure her husband gets a fair trial. She also has been prohibited from seeing him while he's in prison and said he was subjected to "emotional and mental abuse" in the Japanese detention center. Officers left the lights on all day and night, she said, adding that his cell was damp and cold without heat in the winter. She also said her husband was only allowed fresh air for 30 minutes Monday through Friday.
"It's devastating to think he's being treated like, you know, a big criminal over an accusation that we still don't understand what it is," she said.
Ghosn cannot leave Japan under the terms of his bail, which is set at 1 billion yen, or $9 million. The Japanese Ministry of Justice did not immediately respond to a request for comment.
"I think he's devastated that a company that he loved and he worked so hard for could do this to him," she said.
Carole Ghosn also accused Nissan of orchestrating a conspiracy to avoid a merger with French automaker Renault.
"We know it's a conspiracy. Nissan did not want this merger," she said.
"A few people within Nissan decided to get rid of my husband, that was the easiest way not to do the merger," she said. "There was maybe a more civilized way of doing it."
Nissan spokesman Nicholas Maxfield rejected Carole Ghosn's claims, saying, "the sole cause of this chain of events is the misconduct led by [Carlos] Ghosn."
The company also has an entire section on its website dedicated to "executive misconduct" that details the charges against Ghosn and his former deputy, Greg Kelly.
"Nissan's internal investigation has uncovered substantial evidence of blatantly unethical conduct," Maxfield said, adding that the board unanimously voted to oust both men. "Further discoveries related to Ghosn's misconduct continue to emerge."
Ghosn has consistently refused to sign a confession and has accused Nissan and unnamed executives at the company of "backstabbing," and engaging in a "coup."
Nissan reportedly rejected a proposed merger with Renault in April. The offer came shortly after Nissan removed Ghosn from the board, ending his 19 years with the company. The companies are in an long-standing operating alliance with Japan's Mitsubishi that further complicates matters.
Italian-American automaker Fiat Chrysler announced a proposed merger with Renault last week. Carole Ghosn said, "it's clear how Nissan doesn't want to be involved and they want nothing to do with it."
"I think with time, we will see more clarity on this story. And people now realize ... this was a conspiracy against my husband," she said.
Carole Ghosn said she could not discuss the specific allegations against her husband, but said he's innocent. She said she's filed two petitions with the United Nations — one for detention conditions and another for separating husband and wife — and has also reached out to Human Rights Watch.
"I'd like to speak to my husband. I miss him dearly, and I wish I could go and be with him at the hardest time of our life and to take care of him," she said.
Nissan CEO Hiroto Saikawa said Monday that Fiat Chrysler's proposed merger would "require a fundamental review of the existing relationship between Nissan and Renault."
— CNBC's Paul Eisenstein contributed to this report.