Laura Plummer, 33, travelled to the north African country with nearly 300 tablets of tramadol, as well as some naproxen, which she claimed were for her sick partner.
Tramadol is illegal in Egypt and it is widely used as a recreational drug, supplanting heroin and cannabis.
The woman, from Hull, has been detained since she was arrested at Hurghada international airport on the Red Sea on 9 October.
Her family was told she may face the death penalty, or 25 years in jail.
Her brother James said she made an "honest mistake" by bringing the painkillers after learning that her partner was suffering from back pain following an incident.
"They were prescribed to a friend of hers," he told the BBC. "So she took those over with her. Laura didn't even check what they were, she didn't even know there was tramadol in the bag. There was also naproxen as well."
Plummer's family travelled to Egypt to visit the woman, who is due to appear in court on Thursday (9 November). She currently shares a prison c ell with some 25 other inmates.
"They say she's unrecognisable. When they seen her, she's like a zombie, they said," James told the Press Association.
"I don't think she's tough enough to survive it. She has a phobia of using anybody else's toilet, so let alone sharing a toilet and a floor with everybody else. That will be awful for her, it'll be traumatising."
Plummer's father is believed to have spent at least £10,000 on her legal fees.
Karl Turner, PM for Kingston upon Hull, has said that the Foreign Office was involved and that the British embassy in Cairo had provided the woman with a lawyer.
"The family describe Laura to me as somebody who is very naive," Turner told the Guardian. "Her father said to me, 'look, the truth is she wouldn't know tramadol from a Panadol. She wouldn't have a clue that she was doing something unlawful.'
"Her family said to some extent it is better that she's with lots of people in a cell than in a cell on her own because people are around her. But the conditions are going to be extremely basic and I'm sure she's petrified by what is unfolding before her."
Plummer and her husband, Omar, met four years ago. They married by singing a form, which makes the marriage not legally biding in the UK.
Plummer travels to Egypt around four times a year to spend time with her partner, who is already married to a Muslim woman, according to The Sun.