Lissie Harper had been married to PC Harper for just a month when he was killed by Henry Long, 19, and Jessie Cole and Albert Bowers, both 18, as they tried to steal a quad bike.
PC Harper, 28, was dragged for more than a mile along the country lanes of Berkshire when he became entangled in a tow rope attached to the teenagers' getaway car.
Cole and Bowers were convicted of manslaughter by an Old Bailey jury on Friday, but all three defendants were acquitted of murder. Long had previously pleaded guilty to manslaughter.
In an open letter posted on her Facebook page on Tuesday evening, Mrs Harper wrote to the prime minister, home secretary Priti Patel and Lord Blunkett urging them and others "to right such a despicable wrong for our country”.
She wrote: "I implore you to hear my words, see the facts that are laid out before us, and I ask with no expectations other than hope that you might help me to make these changes be considered, to ensure that Andrew is given the retrial that he unquestionably deserves and to see that the justice system in our country is the solid ethical foundation that it rightly should be. Not the joke that so many of us now view it to be.”
The Prime Minister said he will comment on Mrs Harper’s plea once legal proceedings are over.
The letter comes after an online petition to overturn the verdicts received over 200,000 signatures.
The original trial was abandoned the day the country went into lockdown in March, while for the retrial Mr Justice Edis ordered extra security measures amid fears of potential juror intimidation by supporters of the defendants.
A female juror was discharged just a day before the remaining 11 started deliberating on their verdicts after she was seen by a prison officer to mouth "Bye boys" to the teenagers in the dock.
The defendants, who had previously been seen laughing, hugged each other after the verdicts were returned following more than 12 hours of deliberations.
Speaking outside court, Mrs Harper thanked the police and prosecution who had "stood in our corner and fought to make sure these men were made to repent for their barbaric crimes”.
But she criticised the verdicts in the open letter on Facebook.
She wrote: "I will keep fighting on behalf of Andrew, the future that was stolen from us and also the victims who find themselves in this unjustly situation in the future.
"After all, who are we if we allow our legal system to fail us?
"What is this country if it does not provide justice for the innocent?
"What does it say to the public and the police officers, old and new if every day they go out and put themselves at risk to detain these criminals just to witness them be treated so exceptionally lightly in the eyes of the law?
"It says that we are weak, that we will roll over to the despicable thieves and vile miscreants of this world and literally let them get away with murder.”
Long, Cole and Bowers face sentencing on Friday.