Maxine Carr has applied for a tagging scheme that would allow her to be freed early from her three-and-a-half year jail term, imposed after the Soham case.
Carr has protested her innocence
Her application has prompted changes to the Home Detention Curfew scheme.
The Home Office says final decisions to release and tag prisoners will not be made by prison governors in some cases.
Carr, 26, was convicted last month of conspiring to pervert the course of justice following the murders of Holly Wells and Jessica Chapman.
Carr's ex-boyfriend Ian Huntley was jailed for life for the killings of the 10-year-olds.
The HDC scheme sees prisoners released early with electronic tags that set off alarms if a strict curfew is not kept to.
Having already spent 17 months in prison, the vast majority before the trial, Carr would be eligible for release at the halfway point of her sentence, in May.
But if she was successful in her application for tagging, she could be released at any time.
Previously, prison governors made the final decision on who could be released under the scheme, which excludes most violent and sexual offenders.
But now, the government says, decisions on "exceptional cases", including Carr's, will be referred to Martin Narey, the chief executive of the National Offender Management Service, the newly merged prison and probation service.
Former chief inspector of prisons Sir David Ramsbotham told BBC News the rule change was "extremely sensible" as Carr would be "at risk" if released.
But the national probation service union, Napo, says it sets a dangerous precedent.
Assistant general secretary Harry Fletcher warned that the new procedure could allow the press to decide whether or not a high-profile prisoner was released.
"Therefore, I hope it is used sparingly," he said.
Mr Fletcher also said there were also practical problems posed by the HDC application.
"Carr would have to nominate an address for HDC and that would have to be
vetted by probation and the private tagging company," he said
"The more people who know where she is, the more her identity could be
His comments came after prisons minister Paul Goggins said offenders might be considered unsuitable for the HDC scheme if it was thought that granting an application might damage public confidence in the scheme.
"It is for this reason that the home secretary has already made it clear that offenders serving sentences for certain current offences and prisoners with any history of sexual offending must be considered unsuitable for release on HDC," he said in a written parliamentary answer.
But Liberal Democrat home affairs spokesman Mark Oaten told BBC News damage to public confidence would be a "very hard thing to prove and could change from home secretary to home secretary".
He said the decision was a totally unjustifiable "knee-jerk response" to concerns about the tabloid press.
But Prison Fellowship International director Jonathan Aitken told BBC News difficult decisions in "high-profile public-interest cases" should be taken by accountable ministers.
"The buck stops on the home secretary's desk," the former MP, himself released from prison under the HDC scheme, added.