Ms Maxine Carr, accused of perverting the course of justice after the deaths of Holly Wells and Jessica Chapman from Soham, Cambridgshire, faces two new charges.
The Crown Prosecution Service alleges that, knowing school caretaker Mr Ian Huntley had murdered the girls - or committed some other offence - she lied about his and her whereabouts, intending to impede his apprehension or prosecution.
Mr Huntley - accused of murdering the girls - and Ms Carr are both listed for a pre-trial hearing at the Old Bailey at the end of next week. Neither is expected to attend.
The indictment against them was lodged at the court today. It contains the two extra charges accusing Ms Carr of assisting an offender.
The two new charges allege that Ms Carr, knowing that Mr Huntley had committed arrestable offences, provided false accounts of his and her whereabouts and activities at the relevant times.
There is one new charge for each of the two dead girls.
The Cambridgeshire schoolgirls went missing on August 4th 2002. Their bodies were found at Lakenheath, Suffolk, on August 17th.
Mr Huntley has been charged with their murders. He and Ms Carr face a joint charge that they perverted the course of justice.
PA