Lissie Harper had been married to Pc Harper for just a month when he was killed by Henry Long, 19, Jessie Cole and Albert Bowers, both 18, as they tried to steal a quad bike.
In an open letter posted on her Facebook page on Tuesday evening, Mrs Harper wrote to , Home Secretary Priti Patel and Lord Blunkett urging them and others "to right such a despicable wrong for our country".
Lissie Harper said she has her own 'life sentence' after the death of her husband:
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 original trial was abandoned the day the country went into coronavirus 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 said she was "immensely disappointed" with the verdict.
In her open letter, Mrs Harper again criticised the verdicts.
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."
In a statement, a spokesperson for Boris Johnson said: “The prime minister’s thoughts are with the family and friends of Pc Andrew Harper and they have his every sympathy for their loss.“The bravery which Pc Harper showed in intercepting those criminals is a reminder of the risks our police officers face every day to keep us safe.“His courage, dedication and professionalism represents the very best of our police – and of all of us.
"The Prime Minister will respond to Mrs Harper’s letter formally once legal proceedings have concluded.”
Long, Cole and Bowers face sentencing on Friday.