It snuck up on her just like her cancer diagnosis.
The 54-year-old will compete in the 10km race during the Dunedin Marathon event tomorrow.
Her only goal is to just keep plodding forward. She will not break any records and she is hoping the "euphoria of the event" will carry her through the last few kilometres.
But running is her way of taking some of the power back.
If offers a portal she can pass through to escape for a while; that has been a life-saver of sorts.
Ms O’Brien had enjoyed good health until late in 2020, when she received the news she had bowel cancer.
It was a frightening time and the memory ushered in some tears.
It is still a frightening time. She is cancer-free but still in that period where health is carefully monitored and patients live with the thought it might return.
Running helps her manage that anxiety.
"When I’m running, I can’t think of anything else," she said.
"I’m not afraid. I don’t have time to be afraid of anything, I don’t have time to be worried about anything.
"All I have to do is keep breathing and keep putting one foot in front of the other and enjoy the experience of being in my body."
While she was waiting for surgery, she had a lot of time to reflect on what she needed to do to cope with the challenges ahead.
For her that was getting out in nature. She was too fragile to run, so she did lots of walking.
Following surgery she was able to restart running.
Actually, she had never really been a runner.
But just before her cancer diagnosis, she woke up one morning with the sudden urge to go running
— an impulse that came out of nowhere.
O’Brien is now a regular on the tracks around Dunedin, but she still does not see herself as a runner.
It is less about the exercise and more about the experience for her.
"It is about having time to yourself and one of the big things for me was to be outside in nature.
"To be able to be running through bush or trees and being outside," she said tearfully.
"You do things that allow you to feel like you have some sort of autonomy over your health."
"It gives you a strange sense of freedom, because when you are running, it’s difficult but there is also a sense of power with it."
There has been a record number of entries for the events.
As of yesterday afternoon, there were 2588 athletes, eclipsing the previous high of 2369 in 2009.
