Umm Zubeida, who told the BBC in 2018 that her daughter had been forcibly disappeared by security forces and tortured, has been returned to prison despite the fact that a Cairo criminal court ordered her release on Saturday.
The BBC's report "The shadow over Egypt" drew international criticism after detailing widespread disappearances and torture carried out by Egyptian authorities.
Mona Mahmoud faces charges of publishing and broadcasting false news that could harm the country's interest and joining an illegal group; the Muslim Brotherhood, which was listed as illegal in 2013.
This is the fourth time a court ordered Mahmoud's release and she has been returned to prison, over the same charges.
Zubeida Ibrahim Ahmed Younis, who had not been seen since April 2017, appeared on television shortly after the BBC report was aired to say that she had not been kidnapped and tortured by authorities and that she does not speak to her mother due to personal reasons.
In response to the report lawyer Mohamed Hamed Salem filed a lawsuit calling for the closure of the BBC office in Cairo, a ban on its website and the withdrawal of its license to operate in Egypt.
He said the "BBC broadcasts are false news adopting an anti-Egypt rhetoric with the aim of undermining Egypt's stability and economy, while agitating public opinion."
In response to the interview, the State Information Service called on officials not to conduct interviews with the organisation and has asked for an official apology and Egypt's National Media Authority suspended cooperation with the BBC.