She has talked some of her friends into doing the marathon, and with her girls also deciding to do it, she didn't want to be the one left out.
"I had to walk the talk, really. I always said that I thought I would like to have done one more marathon before I was 50. So I'm sneaking it in this year and then that may be it. My body hasn't forgotten how hard those long runs are, as my family will tell you. They hear all about it - too much, I've been told."
Meanwhile Ian, who ran his first marathon at Rotorua in 1984, has been doing them ever since. He has completed 67 and the 50th anniversary will be his 26th Rotorua Marathon.
"Rotorua was my first and it is a great course, well organised and always a good weekend away," he said.
Over the years the trip to the Rotorua Marathon has been an annual holiday for the Chibnalls. Ian is bursting with pride to see his daughters taking on the challenge.
"It is amazing," said Ian, whose fastest marathon came in 1988 in Hastings in 3:04.
"It wouldn't be too often you could get a sporting event that a whole family would want to do. I am proud of them. It's good for them to take on an event that takes them out of their comfort zone. Towards the end, they will be uncomfortable!"
He has bigger goals in mind: "I have pencilled in on my bucket list to complete 100 marathons. It is a race against time versus the body holding out."
His daughters, who have been inspired by their running-mad parents, have time on their side.
Ashleigh-Rose completed her first Rotorua Marathon in 5:46:38 at the age of 18. She described it as a rewarding and a steep learning curve.
"It was a very, very painful and hard experience," she said.
"Running towards the finish line with my Dad and my sister supporting me was the coolest thing ever. "
Ashleigh-Rose said her debut taught her how to look after her body better and the importance of stretching and consistent training.
"I know now too that a lot of it is just a mental challenge so if I do all the training properly, race day will be easier." She is looking to pass on that advice to her younger sister Eilish.
"I'm feeling more excited than nervous," said Eilish.
"I love going down to Rotorua to support my Dad and the other runners so I'm excited to be able to run the race myself."
Both sisters said they are not competitive. They just love to run together. "I really look up to my sister and everything she's done at a young age," said Eilish. "I've seen her push herself past her comfort zone which has inspired me to do the same. We encourage each other in not only our training but in our everyday lives too."
Their parents are quick to stress that getting into running long distance has been their daughters' choice. Eilish said that running long distance makes her feel good, and Ashleigh-Rose said "We are lucky to live in an area where a 32km run is scenic and beautiful and makes training much easier. Distance running takes me to my 'happy place' especially on the longer runs when [university] is stressful."
The training as a family has been great fun. Amanda said the banter has been brilliant.
For their long run on a Saturday morning they all get up at 5am and head out into the Waitakeres.
They don't really run in a group and have their own pace while Ian runs ahead then loops back to the last person then catches up to the first person.
"This year the training isn't doing his running really any good but he's just happy to be doing it with the family," she said. Ashleigh-Rose added: "Last weekend's 24km Dad took me and Eilish out on the hilliest run ever and neither of us talked to him for the rest of the day, that wasn't fun! But Dad always finds our reactions pretty funny, I think."
Ian has offered his girls simple advice as they look to complete the marathon.
"I tell them the race is their own, don't worry about what everyone else is doing, enjoy the scenery, talk to fellow competitors on the way, and most of all enjoy the journey."
Whatever happens, it will be a special day for the family - one that they will all look back on with pride for many years.
Amanda added: "I've always said that to run a marathon is a huge accomplishment and not many people can say they have, so we are quite a unique bunch."
