The woman was taken into custody by police in Hanover on Sunday after a new warrant was put out for her arrest by police in Sweden.
Swedish police said they had found additional evidence linking her to the murder.
Last week it emerged that the woman had been caught on security camera at Arboga train station.
"We believe we have pictures of the woman taken at times we consider important to the case," police spokesman Torbjörn Carlsson told Svenska Dagbladet on Sunday.
Police have not yet been able to speak to the 23-year-old mother of the two murdered children. The woman, who was seriously injured in the attack, awoke on Friday for the first time since the attempt on her life on March 17th.
Police are hoping that she will remember the identity of her assailant.
The 31-year-old suspect was first arrested in Hanover on Maundy Thursday but later released when police did not have enough evidence to warrant a detention.
The German woman was previously in a short relationship with the 23-year-old's boyfriend.