(CNN) -- Time is running out for a British grandmother facing execution for drug trafficking in Indonesia, after her second appeal was rejected.
Lindsay June Sandiford, 56, was convicted in January of smuggling what officials said was cocaine worth an estimated $2.6 million after she was stopped by customs officials at Ngurah Rai International airport in Bali in May last year.
Sandiford, from northeast England, was found to have blocks of cocaine weighing 4.7 kilograms (10.4 pounds) in her suitcase when she arrived on the island on a Thai Airways flight, the court heard during her original trial.
She received the death sentence despite the fact prosecutors only requested a 15-year prison term.
A subsequent appeal against the sentence handed down by Denpasar District Court was thrown out by the Denpasar High Court in April -- a decision that has now been upheld by the country's Supreme Court, according to the official Antara news agency.
"Her appeal was rejected," presiding Judge Artidjo Alkostar said late Thursday, according to Antara.
Three other defendants in the case received jail sentences of six years, four years and a year respectively.
A lawyer representing Sandiford expressed disappointment at the decision.
"We're very disappointed by the Supreme Court's rejection of her appeal. Lindsay was only a courier and a collaborator and cooperated with the police," Fadillah Agus told CNN Friday.
"They were able to arrest the other suspects with her help so she should've gotten the lightest sentence," he added. "The other suspects got off with lighter sentences. We are disappointed but we have to honor the court's decision.
"We have two options, a judicial review or seeking clemency from the president. But I have to discuss this first with Lindsay and see what step we should take."
He revealed he last spoke to Sandiford, who remains in prison in Bali, over a month ago. According to Agus, she was keeping herself busy and socializing more with other inmates and prison officials.
Britain's Foreign and Commonwealth Office, meanwhile, is seeking confirmation of the decision.
"We are aware of unconfirmed reports that the decision of the Indonesian Supreme Court has been announced. We are seeking confirmation of the decision from the Indonesian Supreme Court," a Foreign Office spokesman told Britain's Press Association.
"We will continue to provide consular assistance to Lindsay Sandiford and her family at this difficult time."
Indonesia, the world's most populous Muslim nation, has strict laws against drug trafficking.
The head of Bali's Customs and Excise Agency monitoring division, Made Wijaya, warned at the time of her arrest that Sandiford could likely face execution if convicted.
"The main reason is because narcotics can massively endanger the young and, thus, whoever is caught with drugs should be severely punished. If three people can consume one gram of cocaine, then this operation has potentially saved up to 14,000 lives," he said.
Indonesia has carried out 22 executions since 1998 -- 14 for murder, 5 for narcotics crimes and 3 for terrorism, according to the Lowy Institute for International Policy. Five of the 22 people executed were foreigners; all five were executed for drugs crimes.
According to Lowy, one plea for clemency has succeeded in a capital case since 1990, out of a total of at least 36 pleas.
CNN's Kathy Quiano in Jakarta contributed to this report.