Preeyanooch Phuttharaksa, 23, from Bangkok, told the court in southern Ho Chi Minh City she had smuggled methamphetamine to Vietnam from Benin last October, the Tuoi Tre newspaper said.
She was arrested after the drugs were found in a false bottom in her suitcase.
Preeyanooch said she had been paid 50,000 baht ($1,570) to transport the drugs, the report said.
Communist Vietnam's anti-drug laws are among the world's harshest. There are currently more than 400 prisoners on death row in Vietnam, mostly for cases involving drugs or murder, but executions have declined in recent years.
Five prisoners were executed last year, one for drugs-related offences, according to statistics compiled by AFP.
Since July 2011, when Vietnam changed from execution by firing squad to lethal injection, no prisoners have been put to death.