Australian grandmother Donna Nelson has been dealt a crushing legal blow as she bids to clear her name of a drug smuggling conviction in Japan.

Her lawyers were hoping expert evidence from a Monash University romance scam expert would convince the three appeal judges she was the innocent victim of a romance scammer.

WATCH THE VIDEO ABOVE: Donna Nelson suffers legal blow in smuggling appeal.

Know the news with the 7NEWS app: Download today

But on Thursday afternoon the Tokyo High Court rejected that report and another dozen pieces of evidence Nelson and her team wanted to be considered when they hand down their ruling in September.

Among the Perth grandmother’s supporters in court on Thursday was her eldest daughter, Kristal Hilaire.

“There is a bit of fear in how we think the decision will go,” Hilaire said.

“I think that was going to be a big part in her being able to strongly argue her innocence.”

Nelson’s lawyers said the professor’s report demonstrated the lengths her scammer — who called himself “Kelly” — went to when he tricked her into carrying a suitcase he had hidden meth inside.

“The trial court found that Kelly’s communication was too strange, so she should have known,” lawyer Rie Nishida said.

“But we were countering that by the expert opinion, to show this scam was very sophisticated.

“I still believe we have a much better understanding about how she was scammed, so I hope the judges will too.”

Monash University professor Monica Whitty has researched romance scams for 15 years and said legal systems globally were only slowly beginning to accept the modern online form of the con exists.

“I don’t think they get how they really can work on a victim, to the point they completely do not notice cues, that some might think are obvious, but are not obvious to the victim,” Whitty said.

“What was even more devious in Donna’s case, is that the criminals were so clever to build up a narrative of a businessperson, who was into fashion, and who was into a luggage line.

“Now that might seem odd when someone looks at it as one snippet of time, but if you look over time, and everyone is excited, and there’s a marriage at the end of this, then it makes sense.

“Because he was a ‘fashion designer’, and all of those things, that makes sense for her to carry that bag.”

Nelson, 59, was convicted in December of smuggling 2kg of meth into Japan in a suitcase in January 2023.

For the crime, she was sentenced to six years behind bars.

Nelson, a Perth community leader and one-time Greens political candidate, has always maintained her innocence, insisting she is a victim.

During her trial, she told the court she had no idea the man she believed she was going to marry had hidden the drugs in the case.

Since her arrest, Nelson has also not been allowed to make any phone calls and communication to her family has been limited to brief prison visits and letters.

Nelson will now have to wait until September 25 to learn the High Court’s judgement — whether it accepts her appeal and she is let go, whether the case goes back to trial, or whether the appeal is dismissed and she needs to serve out her six-year sentence.