'We won't just give up': Rouxle Le Roux's victim's mum on failed home detention appeal

Crown Law won't appeal the home detention sentence of the woman who killed Nathan Kraatskow, but his mother says she's not giving up.

Rouxle Le Roux was sentenced to 11 months' home detention and 250 hours' community service after she fatally hit the 15-year-old at an Albany intersection in May.

Her sentencing caused nationwide outrage, and more than 150,000 people signed a petition calling for a harsher penalty. However, on Thursday, Crown Law announced her sentence will not be appealed.

"We consider the sentence imposed on Ms Le Roux was appropriate in all of the circumstances of the case, and there is therefore no basis for an appeal," it said in a statement.

Charlene Kraatskow, Nathan's mother, says it's a setback - but not the end of the road.

"Obviously my husband and myself are quite disappointed, but if they've looked at it and they say they can't do an appeal, I guess there's not much we can do about it," she told Newshub.

"Our petition is still being handed to Parliament; we'll still see if that goes through and if something happens with the justice system, which would be a good thing too."

She says the overwhelming support for her petition proves a systemic change is needed.

"It just shows you that we aren't the only ones who feel something's not right, the sentence doesn't fit the crime," she said.

"But again we're not on the law side of it, so there's nothing more we can do. We can't really go up against the Crown again when they've already made a decision."

Mrs Kraatskow and her husband Orion are determined to make sure something positive comes of their son's death.

"We won't just give up, we're still going to work side by side with the people who helped us down in Wellington to try and get something changed about the justice system and how these cases are looked at and the sentencing that comes with them.

"I still don't think that 11 months of home detention is good enough for killing someone, especially if you've had alcohol and drugs in your system."

She's thankful for New Zealand Police and all the detectives who worked on their case - especially lead detective Kelly Osbourne, who she says has been "amazing".

"We know that this doesn't reflect on them; it's the justice system, and we want them to know they do an amazing job and we're thankful for that."

Mark Mitchell, National's spokesperson for Justice, says he's also disappointed with the Crown's decision.

"We felt very strongly it would reach the manifestly unjust threshold," he told Newshub.

"All we can do, without seeing what Crown Law based their decision on, is sit down and try and work out some legislation to make sure that we reinforce the fact people like Charlene and Orion should be at the heart of these sentencing decisions, and not sitting on the peripheries wondering why they haven't been taken seriously."

He says "strong crime prevention policies" are needed to make sure a similar situation doesn't happen in future.

"If [the Government] sends soft on crime signals, this is what happens. We start to see situations and decisions like this start to arise."

Mr Mitchell says the Kraatskows are "devastated" but should be proud of what they've achieved.

"They've done all that they can, they definitely have the support of the country and they've also made sure the issue has been highlighted so we can look at where the gaps are and fill those gaps with our own bills."

The family faces a tough holiday without their son, and Mrs Kraatskow says they'll be taking a break from campaigning and focusing on caring for each other.

"Right now, we're just going to focus on our girls and our other son and getting through the first Christmas without Nathan, to start healing and move a little bit forward."