Craig said she wanted the decision to be reversed.
“I understand there needs to be changes because the prisons are full to capacity. But that’s not the victims’ fault,” she said.
“Harley Whiteman will come out, he’ll have the rest of his life to live.
“But Kaylan was only 13. I want them to take that into consideration when they’re making these decisions. It’s just wrong.
“If it means building new prisons, then that’s what they need to do.”
She said the family “promised” Kaylan they would get justice for him, and had started a petition calling for Whiteman to be denied early release from prison.
A Ministry of Justice spokesperson said it wanted to “block more offenders from getting out sooner into their sentence”, but that could not happen without “risking prisons reaching capacity and collapsing”.
“If that happened, police could not make arrests, courts could not remand offenders and there would be unchecked criminality on our streets,” it added.
“We are pulling every lever to protect the public and cut crime – building prison places at the fastest rate since the Victorian era, launching the biggest ever expansion of tagging to toughen community punishment and increasing support to victims, giving them a say in the strict licence conditions of offenders.”