Rahaf Mohammed al-Qunun said she fled Kuwait while her family was visiting the Gulf country and had planned to travel on from Thailand to Australia to seek asylum. She said she was detained after leaving her plane in Bangkok and told she would be sent back to Kuwait.
She was scheduled to be sent back on Kuwait Airways flight 412 leaving at 11:15 a.m. local time (0415 GMT).
"My brothers and family and the Saudi embassy will be waiting for me in Kuwait," Qunun told Reuters by text and voice message from a Bangkok transit hotel late on Sunday.
"They will kill me," she said. "My life is in danger. My family threatens to kill me for the most trivial things."
Thai immigration authorities denied Qunun's allegations they were acting at the behest of the Saudi government, saying she was refused entry to Thailand on Saturday night because she did not have the proper documents for a visa on arrival.
A representative from the Saudi embassy in Thailand said there was no one available to comment.
New York-based Human Rights Watch said Thailand should not send Qunun back to her family because she is an adult who faces danger.
"Thai authorities should immediately halt any deportation, and either allow her to continue her travel to Australia or permit her to remain in Thailand to seek protection as a refugee," Michael Page, deputy Middle East director at Human Rights Watch, said in a statement on Monday.
Qunun said she had obtained an Australian visa and booked a flight. She said she planned to spend a few days in Thailand, a popular destination for medical treatment, so she would not spark suspicion when she left Kuwait.
"When I landed at the airport, someone came and said he would process the (Thai) visa but he took my passport. He came back with what seemed to be airport security and said that my parents objected and said I must return to Saudi Arabia via Kuwait Airways," she said.
She said she believed she was stopped after her family appealed to Kuwait Airways. A spokesman for Kuwait Airways said he had no information about the case.
Thai immigration chief Surachate Hakparn said he had had no contact with Saudi officials or Thailand's foreign minister before Qunun's arrival. He said she was denied entry because she did not have a paid return ticket or a hotel reservation."She was over-exaggerating ... She fled her family from Saudi Arabia and arrived in Thailand but she didn't have necessary documents to enter. Thai immigration had to deny her entry," he said, describing such cases as standard procedure.