Police in Rio de Janeiro released this mug shot of the women
The mother of one of two British law graduates arrested in Brazil over alleged false claims they had been robbed says it is a "misunderstanding".
Simone Headley said her daughter Shanti Andrews and friend Rebecca Turner were both "absolutely traumatised".
Reports say the 23-year-olds claimed items had been stolen before police found the belongings at their hostel.
The Foreign Office confirmed two British nationals had been arrested in Rio de Janeiro on 26 July.
The women were due back from a nine-month trip around the world on Tuesday.
It is understood that if they were charged with fraud, they could face a five-year jail term.
Ms Headley, from Frant, near Tunbridge Wells in Kent, said when she spoke to her daughter on Monday that she had been "terrified" and "in tears".
Simone Headley says her daughter Shanti Andrews has never been in trouble before
"She had had a couple of nights in the police cell and she was aware she was going to be transferred to a women's prison," Ms Headley told the BBC.
"It was so difficult. I told her she would get through it and it was a story she was going to tell her grandchildren."
She said both her daughter and Miss Turner were "honest and hardworking" and "had never been in trouble in their lives".
"I think what has happened to the girls is disproportionate to the alleged offence," she said.
"I just hope the Brazilian legal system will show leniency and mercy."
She added she could not comment on suggestions that the arrests were linked to alleged insurance fraud.
Shanti Andrews kept family and friends informed about her trip via Facebook
"The girls had some things stolen and they put a report into the police station," she said. "There was a misunderstanding - a couple of the items they claimed were then found in their luggage."
Miss Andrews' father Alan, who runs a window cleaning business, has gone to Brazil and the family has appointed a solicitor.
The two women, who are thought to have completed their degrees at the University of Sussex in 2007, have already encountered difficulties on their travels.
They were admitted to hospital for several days in Bolivia earlier this year with a suspected stomach parasite.
A Foreign Office spokesman said it was providing consular assistance.
Press reports in the UK and Brazil say the women had claimed belongings, worth a total of £1,000, were stolen during a bus journey from the tourist resort of Foz do Iguacu to Rio de Janeiro.
O Dia, a Rio de Janeiro daily newspaper, reported that the police were suspicious of the women and accompanied them back to their hostel, where they allegedly recovered the items claimed stolen.