A former cellmate of a woman sentenced to death by stoning in Iran, who spent two years in prison with her and accompanied her to the court when she received the news of her punishment, has told the Guardian how the woman, Sakineh Mohammadi Ashtiani, fainted in shock after hearing the verdict.

"It was in mid-November 2008 when the guards woke us up unexpectedly and told Sakineh and me that we should get ready for the court," said Shahnaz Gholami, 42, whose political activities in support of Azari minorities put her in jail for more than four years in Iran. Gholami, an active blogger, is seeking asylum in Paris.

Later that morning, the officials handcuffed Mohammadi Ashtiani and Gholami and took them to the court. Gholami said: "During the 15-minute journey to the court from the prison, she was just worried for her children, but she was not expecting anything even a bit close to the stoning. When we met once again after the court, she was appalled, absolutely speechless."

The 43-year-old mother of two fainted in shock when they returned to the prison, Gholami said. "For days, she was like a ghost wandering in shock, but when she came back to her senses, she just cried and I didn't see her without crying until the last day I spent time with her in prison."

The Guardian brought Mohammadi Ashtiani's plight to international attention on 3 July. Since then the case has drawn condemnation worldwide and a huge number of politicians, human rights activists and celebrities have joined the campaign for her release. In response, Iran has banned local media from reporting on the case.

Gholami – whose comments cannot be independently verified – said Mohammadi Ashtiani was tortured inside Tabriz prison. "Because of her loving nature, even her malicious cellmates kept distance from her, but the guards couldn't let her live at ease. She was flogged as a part of her sentence, but beside that she was beaten up severely by the guards." According to Gholami, Mohammadi Ashtiani has been refused access to writing materials.

"Until that day she was a calm, ordinary woman whose beauty made prisoners and the guards jealous. She didn't like trouble with other women in the block we were kept in, and because of that she was always alone," Gholami said.

Since May 2006, Mohammadi Ashtiani has been kept in room four of the eighth block of Tabriz prison, in the capital of Iran's East Azerbaijan province. She shares a room with 25 women who are mostly accused of murder. She was originally sentenced to 99 lashes for adultery, but her case was reopened when a court in Tabriz suspected her of murdering her husband. She was acquitted, but the adultery charge was reviewed and the death penalty handed down on the basis of "judge's knowledge". In Iran, officials consider adultery worse than murder, Gholami said.

"To be among those murderers and live with them is a daily torture for Sakineh, whose tender nature had made her exceptional in the block for everyone," Gholami said.

Iran's judiciary has since changed the sentence, following the international outcry, to execution by hanging "because she is convicted of murder". However, a copy of the document detailing the stoning sentence, which was disclosed to the Guardian by Mina Ahadi, of the Iran Committee against Stoning (ICAS), shows that she was convicted of adultery, not murder.

Ahadi said: "In adultery cases, women are sentenced because of the complaints from their husbands or families generally, but surprisingly, Sakineh is sentenced to death by stoning not because the family of her husband have made a complaint against her, but because the Tabriz prosecutor has made a complaint. In other words, it's the authorities in Iran who want Sakineh to be stoned to death."

Ahadi, who is in regular contact with the families of women sentenced to stoning in Iran, has been told recently that Mariam Ghorbanzadeh, 25, a current cellmate of Mohammadi Ashtiani who has been sentenced to death by stoning, is pregnant. The sentence has not been changed.

After a short visit to his mother in prison last Thursday, Mohammadi Ashtiani's son Sajad told the Guardian that she fears she may be executed without prior notice to her lawyer, especially now that Iran has issued an arrest warrant for Mohammad Mostafaei, the lawyer who represented her until recently. Mostafaei is believed to be hiding from officials after his relatives were imprisoned.