A Sydney woman facing the death penalty in a Malaysian drugs case does not yet realise how grave her situation is, her lawyer says.

Maria Elvira Pinto Exposto, 51, from Liverpool, will appear in court in Kuala Lumpur on Friday where she will likely face charges of carrying 1.5kg of crystal meth into Malaysia, which carries a mandatory death sentence.

Her lawyers say the suburban mum is a "naive and innocent mule" who has been duped.

Lawyer Tania Scivetti says her client thought she was carrying documents from Shanghai to Melbourne for her boyfriend, a US soldier about to retire from service in Afghanistan.

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"When the drugs were found in the bag, she was very surprised," Ms Scivetti told AAP.

"She'd never seen drugs in her life."

The mother of four is physically well and has access to her medication for diabetes, the lawyer says, but she doesn't realise the gravity of her situation.

"She asked me how long is this going to take and I said quite some time, and she was really down," she said.

"I don't think it's really hit her yet, what's going on.

"As the facts stand it's a tough, but not impossible, case."

Airport customs authorities say they found the ice, worth more than $100,000, in a secret compartment stitched into the backpack.

Mrs Exposto was only supposed to transit in Kuala Lumpur but mistakenly followed the passengers who got off her flight from Shanghai and had to go back through customs and immigration again.

There, she volunteered her bag for scanning, customs says.

Earlier this year, the same legal team successfully defended Perth truck driver Dominic Bird, who was acquitted of charges of selling 167g of ice to an undercover police officer in Kuala Lumpur in 2012.