Laura Plummer was arrested in October after being found with 290 tramadol pills in her suitcase.
Plummer's trial started in the town of Safaga on Monday with what her lawyers described as a mistaken confession.
Her family have insisted she has been treated fairly by the Egyptian justice system, which will today decide whether to postpone her hearing or accept a bail offer.
Ms Synclair said: "She's absolutely terrified, she's petrified. she looks shocking, she looks shock white, her hair has fallen out, her teeth are all discoloured, she's got a rash all over her face, she couldn't even stand up in court".
Tramadol, a prescription opiate and painkiller, is banned in Egypt and is used as a recreational drug for its cheap price and relaxing, re-energizing high, as well as its supposed aphrodisiac qualities. "She doesnt deserve that", Rachel said. "I was anxious about her staying in the police custody; now she will be in the prison with criminal people".
Sister Rachel Plummer said: "My mum's obviously devastated". Were just hoping. Even half of that would be better.More news: Parents Angry While Ivanka Trump Surprises Visit Connecticut High School
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"After she was sentenced to three years, she was then put in a cage, like an animal".
She says she has no idea what she doing was illegal and was just "daft" after being given the Class C painkillers by a work friend. When you go to see Laura, she's in a mess - how can you do this to a young girl?
Her lawyer Mohamed Othman said a plane ticket which showed she paid twice as much for her flights as the drugs were worth shows she was not looking to sell them.
She said her daughter was being held in awful conditions in a cell with no beds, sharing with up to 25 other women.
"I am hopeful that good sense will eventually prevail", he told BBC Radio 4's The World At One.