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The 39-year-old police inspector, who only took up the sport in 2012, has enjoyed some promising results in the past year and has been tipped as a title contender in the race.
Aitken came second in the women's Christchurch Marathon in May last year and broke the 2hr 50min mark for the first time, finishing in 2hr 49min 13sec.
She went backwards a little in last November's Auckland Marathon, finishing fifth in 2hr 55min 44sec, but will enter tomorrow's event as one of the favourites, along with Palmerston North's Klaartje van Schie, Auckland's Katie Wyrill and former Olympian Liza Hunter-Galvan.
Hunter-Galvan attended the 2004 and 2008 Olympics but was banned from racing for two years in 2009 for taking a banned substance.
Aitken is not putting any pressure on herself to claim a top-three finish and said she would run her own race.
She had run the Rotorua Marathon once before, finishing third in the 35-39 age-group in 2014 in 2hr 59min 31sec.
The race marked the first time she had broken the 3hr mark.
"I'd absolutely love to get a placing but, at the end of the day, I run for the best I can do.
"If I get placed, that's great, but I'll have my own personal goals that I want to achieve.''
Aitken, who is currently based in Greymouth, had no specific target in mind for the race but wanted to finish around the 2hr 50min mark.
"I don't want to put a specific time on it, but I'd want to be improving on what I did two years ago.''
Aitken usually trains six times a week, covering an average of 100-140km.
Her work days could be long and there was no guaranteed finish time, so she usually got her training in before work.
She often competed in local events during weekends.
Despite the seemingly heavy schedule, it was not difficult to find time for training, she said.
"I think that's because of the fact I've found something I love and I'm passionate about.
"If you had said to me a few years ago I'd be running marathons, I wouldn't have believed you.
"But I did one and then got the bug.''
Aitken has also taken a liking to off-road racing recently.
She has won the Motatapu Marathon women's race for the past two years and claimed the women's Big Easy Mountain Marathon in Wanaka for the past three years.