Mrs Griffiths was left relieved however when judges kicked out Cooper's claims, insisting he deserved a long sentence because he appeared 'proud of what he had done'.
Cooper attacked mother-of-two Miss Stuart in August last year and stabbed her friend David Roberts who tried to intervene.
Her mother said: 'He's not even a person any more. I can't hate him because he's non-existent.. I will never forgive him.
'He was given 25 years for killing Laura and six years for what he did to Dave. They can only reduce his sentence to 25 years on appeal but it would make a mockery of what Dave went through.
Mrs Griffiths, 55, said Cooper sent her daughter 421 texts in just one day as part of his campaign of abuse before the killing.
She added: 'Police need to recognise these situations. Surely there is something you can put in place on someone that is harassing someone.
'He didn't just do it to Laura. He did it to me and to her daughter. He said the most awful things on the phone to her. She was just 14.'
After the murder, Cooper told a witness: 'I said I was going to do it - and I did'.
He denied murder, but was convicted at Mold Crown Court in March and was jailed for life, with 31 years to serve before seeking parole.
His lawyers today asked appeal judges to the minimum term to allow Cooper to apply for parole sooner.
But three of the country's top judges sitting at the Court of Appeal in London rejected the claims.
Dismissing the appeal, Lady Justice Hallett, sitting with Mr Justice Stuart Smith and Mrs Justice May, said 31 years was appropriate for the terrible murder.
Lady Justice Hallett said: 'He caused huge distress and grief to many people, including two children who must grow up without their mother.
'Far from showing remorse, he appeared to be proud of what he had done.'
An Independent Office of Police Conduct (IOPC) investigation is still ongoing into 18 reports made to the force involving Laura or Cooper prior to her death.
