LONDON—The mother of Shannon Matthews was being questioned by detectives after spending the night in custody, police sources said on Tuesday.
Karen Matthews, 32, from Dewsbury, West Yorkshire, who was arrested on Sunday, is being held on suspicion of perverting the course of justice.
Detectives have been granted an extension to allow further questioning until Wednesday morning, when she will have to be charged or released.
"Detectives investigating the disappearance of a nine-year-old girl in Dewsbury in February are continuing to question a 32-year-old woman this morning," police said in a statement.
"She remains in police custody after being arrested on Sunday on suspicion of perverting the course of justice."
The nine year old disappeared after a school swimming trip in February, sparking a massive police hunt.
She was found safe and well in the base of a bed about a mile from her home 24 days later.
Her mother was the fourth member of the extended family to be arrested in connection with the disappearance.
A fifth member, Matthews' partner Craig Meehan, 22, was remanded in custody on charges of possessing indecent images of children.
Michael Donovan, the 39-year-old uncle of Meehan, has been charged with abduction and imprisonment in the case.
He was taken to hospital on Sunday after a case of "serious self harm", a Ministry of Justice source said, but has since returned to Leeds prison.
Two other family members were released on police bail on Saturday pending further investigations.
Media reports identified the pair as Amanda Hyett, 25, and Alice Meehan, 48, the sister and mother of Craig Meehan.
Hyett was held on suspicion of assisting an offender while Meehan was arrested on suspicion of attempting to pervert the course of justice.
Shannon herself has not returned home since her rescue and remains in the care of social services.
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