Mrs Kaur said her son was in intensive care for a month-and-a-half, at Auckland's Starship Hospital for five months, and had been at the Wilson Centre for Children in Takapuna for nearly eight months.
"He's doing very well - he's a very brave boy. I hope he can walk again."
Prabhjot Singh would be in Year 9 at Katikati College.
Mrs Kaur said both her children were born in New Zealand, and her son dreamed of a career as a rugby player. Daughter Jasnoor was a Year 4 student at Katikati Primary.
Mrs Kaur used to work 25 to 30 hours per week as a grader in a kiwifruit packhouse. She spent any "extra" time with her kids, taking them to the park and to the temple.
She said her daughter was cute and smart, that Jasnoor was reading at the same level as her older brother, and would often write little books about places she had gone.
"She loved dancing also."
Mrs Kaur moved to New Zealand 14 years ago from Punjab, India. She praised her Katikati friends, who were storing the family's belongings, bringing home-cooked Indian food and visiting when they could.
"They're all very busy now because of kiwifruit season," she said.
Forty people have been killed or seriously hurt the past five years on the section of SH29 where Jasnoor lost her life and her brother lost his mobility.
The road will soon become the first trial site for weather-triggered speed signs.
NZ Transport Agency Senior Safety Engineer Adam Francis said 22 electronic signs between SH28 junction and Soldiers Rd would be erected within two months. Three people died on the 12-kilometre stretch through the Kaimais last year.
Mr Francis said the signs worked by relaying information from a weather station that detected factors including rainfall, wind speed and visibility. The new limit was posted on electronic signs and could be enforced by police.
Mrs Kaur said she, her husband and son had been staying in a villa at the rehab centre. They received financial help from ACC. Mrs Kaur said her husband was not working at the moment, and her employer at the packhouse had said she could return to work when she was ready.
"Maybe we go home in two weeks, but I'm not sure."
Prabhjot's regular rugby practice had been replaced with hours of daily physiotherapy. He was allowed an hour and-a-half of school per day and met with a child play specialist each week.
The teen had to manage not only the hard work of rehab, but the knowledge his sister was gone.
His mum said: "He's missing her very much because they grew up together and playing together and especially when it's her birthday."
Mrs Kaur hoped new speed signs through the Kaimais would prevent more deaths, saying it could stop accidents and slow "crazy" drivers who went too fast.
"I'm scared at the moment when we're going somewhere," she said.
Western Bay of Plenty road policing manager Senior Sergeant Ian Campion said the area in winter frequently experienced snow, fog, ice, drizzle and heavy rain.
Mr Campion said: "Installation of that equipment will increase safety by prompting drivers that there's a lower speed limit in force because of weather conditions. "It's not an easy piece of road to negotiate. In the past, there have been far too many crashes on that stretch of road.
"This initiative will hopefully get people to slow down and take notice of weather conditions."
NZTA data showed more than 70 per cent of crashes on the Kaimai Range happened in wet weather, and more than 40 per cent were caused by speed.
The agency said it had already made improvements to the SH29 corridor, including side barriers, a wide centre line and right-hand turning bays.
The Kaur-Singh family said they hoped other families could be spared their pain.
Mrs Kaur said, "My daughter is very special to me. I feel sad and sometimes I can't believe she's gone.
"I have to go to therapy to help me."
Meanwhile, she hoped rehab, time and a mother's love would heal her son.
"I pray to God that my son would be walking again.
"That is my dream. I pray to God he can help us."