Karen Matthews was arrested by detectives on Sunday night
The mother of Shannon Matthews has been arrested by police investigating the nine-year-old's disappearance.
Karen Matthews, 32, was arrested in Dewsbury on suspicion of perverting the course of justice.
Meanwhile, the man accused of abducting Shannon, who was found safe on 14 March, has been treated in hospital after a "serious case of self harm".
Michael Donovan, 39, was later taken from hospital back to Leeds prison where he is currently on remand.
The three-week search for Shannon ended when she was found hidden in the base of a bed in a flat on 14 March - 24 days after she went missing.
Conspiracy to pervert the course of justice can cover a wide range of actions but one suggestion is that when Shannon first disappeared, Ms Matthews might have known more about her daughter's whereabouts than she told police.
Detectives however, are not confirming if this is the case.
Mr Donovan of Lidgate Gardens, Dewsbury, West Yorks, was arrested in March when officers found the Leeds schoolgirl in Batley Carr - a mile from her home.
He faces charges of kidnap and false imprisonment. A provisional trial date has been set for 11 November.
Shannon Matthews went missing for 24 days before being found
A Prison Service spokesperson would not confirm the details of the incident but said: "A prisoner from Leeds was taken to outside hospital overnight following a case of serious self-harm.
"Staff responded to the incident promptly and with great professionalism and the prisoner has now been returned to HMP Leeds."
Mr Donovan, who was formerly known as Paul Drake, is the uncle of Shannon's stepfather Craig Meehan.
Two other women, 49-year-old Alice Meehan, the mother of Shannon's stepfather, and his sister, 25-year-old Amanda Hyett, were held on Friday.
Ms Hyett, of Moorside Road, Dewsbury Moor, was arrested on suspicion of assisting an offender while Ms Meehan was arrested on suspicion of attempting to pervert the course of justice. Both were released on police bail.
In a separate inquiry, Craig Meehan was remanded in custody by Dewsbury magistrates last Thursday after being arrested on suspicion of possessing indecent images of children.