Ann-Marie Kemshell, who previously ran the marathon in 2015, says she promised her boyfriend's father before he died that she would put her running shoes on again to warn people how diabetes affects your life.
"I have been warned about diabetes and how it affects your life," she said. "I never got the chance to meet my grandmother on my dad's side because of diabetes.
"My uncle died at the age of 52 because of it. And my dad suffers with it - thankfully, he manages it quite well.
"I'm quite lucky so far it hasn't affected me but I try to look after myself.
"But then James Clarke came in my life as he was my boyfriend's dad. He was diagnosed with many health issues. One of them was diabetes and it had to be managed by diet.
"Unfortunately, he passed away June 20. He became a big part of my life and is truly missed. Before he passed away, I promised him I would run a marathon in his honor and, thankfully, I get a chance to raise money for a wonderful charity as well."
This year's London Marathon, takes place on Sunday, October 3.
Every year, more than 40,000 people of all ages and abilities run the 26.2-mile (42.2km) marathon through the streets of London.
Some run for personal achievement, some to raise money for their favourite charity, and many run in outrageous fancy dress: from a giant shoe and a London bus, to superheroes and a wide range of animals.
Ann-Marie Kemshell, who works at Hames Chocolates Ltd, says her boss Carol Oldbury was especially excited when she earned a place in the event.
"Carol has been showing a keen interest in my training - she’s an amazing boss," said Ann Marie, who lives in in Ailby near Alford.
"I’ve been running short distances (15-17miles ) for a while now hoping to get a placement in the London marathon.
"I ran the London marathon in 2015 and got a placement for 2016. However, I had to pull out due to glandular fever.
"I was really gutted and had trained twice a week to get ready for it. I’ve been trying to get a placement since but had been unsuccessful."
Previous running experience also includes running the Sea Bank Marathon three times, and the Yorkshire Three Peaks three times, coming fourth overall and being the first woman back on her last entry.
"Training is intense as I don’t class myself as a runner and nothing special," she said. "I do envy the athletes at the Olympics, as they make it look easy, although I hate having ice baths but it enhances the recovery process.
"I have chosen a 24-mile route which has hills up to the 15th mile and the rest is flat. I have the best running partners and they come with me all the way.
"Nika and Finn are possibly fitter than me. They keep me going even through the tough moments when I want to qui - they are my strength.
"And then I have a amazing boyfriend Adrian Clarke, who meets me at a certain point on his bike with goodies then cycles back with me. He’s my hero at that point and shows encouragement and support all the way. He kept pushing me to apply even when I gave up hope.
"I also made a promise to his dad before he died that I would run in his honour and I’m keeping that promise to make him and his dad proud."