Shah Alam, Malaysia (CNN) Malaysian prosecutors rejected an appeal to drop a murder charge against one of the two women accused of using the deadly nerve agent VX to murder the half-brother of North Korean leader Kim Jong Un, just days after allowing her co-defendant to walk free.

The decision means that Doan Thi Huong of Vietnam will remain as the only suspect in the case still behind bars.

Huong was one of two women charged with the February 2017 murder of Kim Jong Nam, an offense punishable by hanging. The other, Indonesian national Siti Aisyah, was freed Monday in a surprise ruling and returned to Indonesia hours later.

Prosecutors did not reveal why they rejected Huong's appeal but let Aisyah go free.

Huong's legal team had petitioned prosecutors to release her on the same grounds as Aisyah, arguing it would be unfair to free one of the co-defendants but not the other.

However Huong told reporters through an interpreter that she wasn't bitter Aisyah was freed and she was not.

"God knows me and Siti Aisyah didn't do anything," Huong said, according to her interpreter.

Vietnamese national Doan Thi Huong, center, is escorted by police as she arrives at Shah Alam High Court in Shah Alam, Malaysia, on Thursday.

After the ruling was announced, Huong wept and pressed Vietnamese ambassador to Malaysia Lê Quý Quỳnh's hands to her forehead.

Quỳnh later told CNN that the Vietnamese justice minister had sent a letter to Malaysia's attorney general requesting Huong's release.

"She's a little bit nervous and weak," Quỳnh said.

Vietnamese ambassador Le Quay Quynh told me he was very disappointed that Malaysian authorities didn't release Duon Thi Huong. The Vietnamese woman faces a possible death penalty for the suspected murder of Kim Jong Nam in Kuala Lumpur airport in February 2017 pic.twitter.com/dWknQ5egJ2 — Ivan Watson (@IvanCNN) March 14, 2019

He said Hanoi would again request that Malaysian authorities treat Huong fairly and release her "as soon as possible."

Huong's lawyer, Hisyam Teh Poh Teik, called the decision not to drop the case "disappointing" in court Thursday.

"The decision not to withdraw does not sit well with our criminal justice system. There is discrimination as the prosecution favors one party to the other," he said.

"Both presented same defense before this court ... The public prosecutor has not acted fairly."

Judge Azmi Ariffin adjourned court on "humanitarian grounds," saying Huong appeared "not well." He then ordered a doctor evaluate her.

Court will resume on April 1.

The other suspects

Four North Koreans who fled Malaysia for an unknown destination shortly after the assassination were also charged in absentia with the murder. The international police organization Interpol has issued red notices asking governments around the world to send them back to face trial.

Analysts said if North Korea was behind the killing, Kim Jong Un may have seen his older half-brother as a potential leadership threat -- even though their father, former North Korean leader Kim Jong Il, had long discounted Kim Jong Nam as a possible successor.

Kim Jong Nam fell out of favor some two decades ago and lived in self-imposed exile in the Chinese-controlled territory of Macau.

JUST WATCHED 2017: Theories behind Kim Jong Nam's murder Replay More Videos ... MUST WATCH 2017: Theories behind Kim Jong Nam's murder 01:43

North Korea has consistently denied involvement in the killing, though US, South Korean and Malaysian authorities have said Pyongyang was responsible.

Huong, Aisyah and the four North Koreans were accused of exposing Kim to the VX as he entered an airport in Kuala Lumpur on the outskirts of the Malaysian capital, killing him in minutes. Prosecutors alleged that Huong and Aisyah wiped Kim's face with the chemical before washing themselves. The North Koreans then promptly left the country.

Lawyers for the two women argued they were duped by the North Korean agents, who tricked them into thinking they were taking part in a reality TV show.

Malaysian authorities disagreed. During the police investigation and through most of the trial , police and prosecutors were adamant that both women knew what they were doing, which made Monday's developments all the more surprising.

Vietnamese national Doan Thi Huong (center) is escorted by Malaysian police after a hearing at the Shah Alam High Court on Monday.

Indonesia lobbies for Aisyah

Indonesian authorities said earlier this week that Malaysia had agreed to release their citizen due in part to intense lobbying by Jakarta. Indonesia's Law and Human Rights Ministry sent a formal letter to Malaysian Attorney General Tommy Thomas, to which he responded on Friday last week.

Aisyah told CNN in an interview, Wednesday, that she agreed to take part in the reality TV show as side job to make some extra money. She said she was offered the job by a Malaysian man and ended up earning about $120, but declined to speak at length about the case.

"My message to the other woman workers, please don't easily trust the others. If you want to do something, you have to understand what is that exactly," she said.

Siti Aisyah speaks at a news conference in the Indonesian Embassy in Kuala Lumpur on Monday.

After Aisyah's release on Monday, Vietnamese authorities appeared to step up their own efforts to free Huong.

Foreign Minister Pham Binh Minh urged his Malaysian counterpart Tuesday to "ensure fair judgement for Huong & to set her free," according to an image tweeted by his ministry.

DPM/@FMPhamBinhMinh held a telephone conversation w/ @MalaysiaMFA FM Saifuddin Abdullah on Mar.12 to discuss several issues in bilateral ties.

Regarding the case of 🇻🇳citizen #DoanThiHuong, DPM/FM asked the Malaysian side to ensure fair judgement for Huong & to set her free pic.twitter.com/ZU4Ja8nfvY — Viet Nam Diplomacy (@MOFAVietNam) March 12, 2019

Vietnamese authorities had been tight-lipped about the case. They did not disclose whether Huong's detention was discussed during Kim Jong Un's visit last month to Hanoi, where he met US President Donald Trump and Vietnamese leaders.

Those meetings would have been unthinkable back in 2017, when Kim Jong Nam's assassination was widely seen as evidence of his half-brother's brutal but calculating leadership style. It was not until the following year that Kim Jong Un made a dramatic foray into diplomacy, holding his first historic summit with Trump in Singapore and also meeting the leaders of South Korea and China.