PC Harper, who was 28, was fatally injured after being dragged for a mile behind the men's car along a country road while responding to a burglary in Sulhamstead, Berkshire, in August 2019.
He was trying to stop the group towing away a stolen quad bike.
It comes as Prime Minister Andy Burnham ordered a review of the early release scheme policy.
PC Harper latest
Henry Long, Jessie Cole and Albert Bowers were jailed in 2020 for manslaughter.
Long, who was driving the vehicle which caused PC Harper's death, received a 16-year sentence, and will not be eligible for the scheme.
Cole and Bowers, who were 17 at the time of the incident, were passengers in the vehicle. They were given 13-year prison sentences but might be eligible for release halfway through, the Ministry of Justice (MoJ) has said.
Our future 'was stolen'
Lissie Harper said in a statement on Wednesday: "It has taken me years to rebuild a life that was torn apart in a matter of moments. Years to pick up the pieces left behind by three men whose actions robbed Andrew of his life and stole our future.
"Now - once again - politicians are making decisions from behind a desk that will have real and lasting consequences for victims' families like mine."
"It is deplorable to me that we have reached a point where releasing prisoners early is even considered acceptable. We speak of justice, accountability and standing with victims, yet decisions like this do the opposite.
"They tell victims their suffering matters less, and offenders that the punishment handed down by our courts is no longer what they will actually serve."
The Police Federation for England and Wales has condemned the prospect as "disgusting".
Its deputy national chair, Brian Booth, said: "Police officers from across the country stood side by side to honour Andrew Harper at his funeral. They and every serving officer will be utterly sickened at the prospect of Bowers and Cole being back on the streets so soon."
'It feels like an insult'
PC Harper's mother, Debbie Adlam, told The Telegraph she had received a letter from the department informing her the sentences may be reduced.
Ms Adlam told The Telegraph it "makes me feel sick" that Cole and Bowers may be released. "It feels like a slap in the face and an insult," she added.
The potential release of Cole and Bowers would come under the Sentencing Act. Set to come into force in September, the legislation stands to see 6,000 prisoners released early.
The policy has proved controversial, but the government has repeatedly said it must act to free up jail cells.
Whole policy 'to be reviewed'
Prime Minister Andy Burnham said he would "review the whole of this policy", and clarified that the "main perpetrator will not be subject to any early release", referring to Long.
He added that inaction in addressing the pressure on prisons a "decade ago" had "created an unacceptable situation now".
"But I want to assure myself that everything has been looked at before this policy proceeds, and I can give that assurance that every single part of this I will look into with the Justice Secretary," he said.
"I can't say that I can't change the policy completely, but I will look at it in detail before we go further forward."
An MoJ spokesperson said: "This was a horrific crime, and our deepest sympathies are with PC Andrew Harper's family and friends.
"In 2024, the country was facing a prison crisis and a total breakdown of law and order, with judges ordered to stop jailing dangerous criminals.
"This government is committed to public safety: we are building prison places at the fastest rate since the Victorian era and taking the difficult decisions needed to lock up the most dangerous offenders."
Following his death, PC Harper's death, Ms Harper successfully campaigned for legal changes to see harsher sentences for the manslaughter of emergency workers on duty.
Harper's Law introduced mandatory life sentences for anyone who commits the manslaughter of an emergency worker on duty, including police, prison officers, firefighters and paramedics. But the legislation was not retrospective, meaning PC Harper's killers cannot have their sentences extended.
Possible release 'feels wrong'
Thames Valley Police Chief Constable Jason Hogg said PC Harper's death has had a "lasting impact".
"Under the law that bears Andrew's name, if his killers were convicted today, they would be receiving life sentences.
"For this reason, for them to be released early under the new Sentencing Act legislation feels wrong. I have written to the prime minister, the home secretary and the justice secretary to make my opinion on this clear."
The backlash to the early release of PC Harper's killers comes as the new defence secretary, Wes Streeting, had to apologise for making a joke about the controversial scheme.
