Attempts to deport one of two twin sisters to their native Uganda failed when she was considered mentally unfit to fly, campaigners have said.
The 20-year-old, who had been living in north London, was booked on a flight from Heathrow Airport on Saturday. Her sister also faces deportation.
Campaigners said it was a "punishing and inexplicable act" to separate the women who have no relatives in Uganda.
The Home Office said it would not comment on individual cases.
The two women have been living in Edmonton and studying at Enfield College since they came to the UK three years ago.
Campaigners claim she was abducted, tortured and saw her mother shot dead while living in Uganda.
According to the women, their case for asylum collapsed last year and they were sent to Yarls Wood detention centre awaiting deportation.
One of the twins' supporters, Henry Wood, said she became so upset at the prospect of leaving her sister and returning to Uganda that she was taken off the flight on Saturday.
"They don't have any relatives that are known to be alive or remaining in Uganda.
"We don't know why, when there are reported human rights difficulties in Uganda that they would deport them separately to that country."
Mr Wood said lawyers were pursuing a civil case against the Home Office for wrongfully detaining the women.