9 March 2017 Last updated at 17:03 GMT
The 19-year-old from Dublin is a competitive runner - but her chronic epilepsy means she has around 16 seizures a day, often during races.
When other competitors see her fall to the ground, they naturally believe she needs to go to hospital - even though she normally recovers immediately and in her case, there's no need for medical intervention.
Even though she's grateful for the public response, all Katie wants to do is carry on running.
When she told the neurologist who's treating her condition, he offered to become her running partner - and together they've become a marathon-running team.
Video by Andy Brownstone and Daniel Gordon

The homes are planned to be for social or mid-market rent and it is hoped they will all be completed by 2021.
Glasgow City Council's executive committee also approved £20m to improve existing housing.
Of this, £14m was announced last month as part of scheme to upgrade homes and make them available for social renting.
The £34m four-year improvement and repair scheme is also being funded with £20m from the Scottish government.
The funding to build homes is to be channelled through housing associations over the next four years.
Eight sites in the area have been identified for development.
As part of the strategy, Govanhill Housing Association has also committed £3.7m to new housing and repairs for the duration of the four year period.
Overall this means there are plans to invest more than £44m in housing in Govanhill over the next four years.
Councillor George Redmond: "This is an impressive document and points to the way ahead in Govanhill."
"Significant sums are being invested in Govanhill and it is great news that part of that money will go towards new housing.
"The council has been working exceptionally hard to turn things around in Govanhill and we are starting to see real progress being made."
He said that while the council was keen to work with all property owners in Govanhill, he warned the council would use power of compulsory purchase against those who refused to get on board with the plans.

Jamie Dimon, the chief executive of JP Morgan - which employs 16,000 people in Britain - has already said he will move hundreds of people out of the UK when it leaves the EU to Dublin and Frankfurt where it already has operations.
Today in Paris he went further.
He said there had been too much focus on what would happen on day one after Brexit. Ominously for the UK, he said that how many more jobs would go to centres all around the EU was no longer in the UK's control.
"What happens next is totally up to the EU, it's not up to Britain. And so once you have that first step, if the EU determines over time that they want to start to move a lot more jobs out of London into the EU, they can simply dictate that. The regulators can dictate it, the politicians can dictate it."
France's former President Francois Hollande once labelled finance "the enemy". Today the Prime Minister Edouard Philippe - speaking at the same event - promised that era was over.
Lower personal and corporate taxes, making it easier to hire and fire, English law courts conducted in English, and three brand new English-speaking schools are among the incentives on offer to bankers prepared to relocate.
Another heavyweight banker, HSBC chief executive Stuart Gulliver, welcomed the proposed reforms.
He has already said he will move up to 1,000 bankers to Paris but he also expressed some reservations - saying it would take time to forget how reviled they were in France.
But under new President Emmanuel Macron it seems France means business with its pro-banker message and as Jamie Dimon said today, his ears are wide open.

The 30-year-old from Holywood, 32nd in the marathon at the Rio Olympics, took ninth place in the Welsh capital.
Pollock finished with a time of 65.53 in a race won by Shadrack Korir of Kenya in a course record of 60.54.
Medical doctor Pollock was returning to Cardiff where he ran a superb 62:46 to finish 14th at the World Half Marathon Championship.
In July, Pollock was the top Irishman in the half marathon at the European Athletics Championships in Amsterdam as he took 17th place with a time of 1:04.28.
Last weekend, Pollock ran his first race since the Olympics when he won the Aurora 10k in Bangor.
Katie Cooke has a lifestyle clash few others can rival.
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About 350 homes are to be built in the Govanhill area of Glasgow under a £6.4m council initiative to help "turn the area around".
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In capital cities around Europe there is a smell of blood in the water - a sense that the UK's financial services industry has been wounded by Brexit and that presents a chance to take a bite out of its dominant position.
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Northern Ireland's top distance runner Paul Pollock claimed a top 10 finish in Sunday's Cardiff Half Marathon.