“Every day it feels like I’ve run three marathons.”

That’s how Katie Kelly O’Donnell describes the extreme exhaustion, physical and mental, that she has to cope with every day. “It’s hard to explain,” she says. “I’ve actually run a marathon before, and I’ve never felt nearly as tired as this.”

Her fatigue is a symptom of multiple sclerosis, the chronic autoimmune disorder against which Katie, 42, has fought a constant battle since she was diagnosed in February of 2016. At the time, the Neponset native was a third-grade teacher at the Condon School in South Boston and mother of a 15-month-old daughter, Áine.

At first, Katie’s doctors and family alike were hopeful that she would be able to continue her daily routine as normal, more or less. But her condition kept worsening, and new tests revealed a far more aggressive form of RRMS (Relapsing Remitting Multiple Sclerosis) than initially diagnosed. Soon, she was feeling the effects of the disease everywhere in her day-to-day life.

“I had terrible headaches, I was forgetting things, and my balance got so bad I had to hold onto desks at school,” she said. Recurring instances of blurred and double vision meant she could no longer drive.

Nevertheless, Katie persisted. As her mother and those close to her know, “Katie is a fighter.” Seven months after her diagnosis, she completed the Boston Athletic Association’s Half Marathon, running 13 miles through the rain with a friend.

Despite the debilitating effects of the RRMS, which effectively amount to a continual state of fatigue and pain, she has returned to work on a modified schedule of three days a week. When asked where she finds the strength to keep teaching, Katie pointed to her students as a source of inspiration.

“I go to work because I love the kids and feel that I do make a difference in their lives,” she said. “I do it for myself, I do it for my daughter. Honestly, I do it because I don’t have a choice.”

Treatment so far has called for regular doses of steroids and the MS drug Tysabri, but after another flare-up in March of this year that saw her symptoms worsen further, Katie and her family decided to pursue other options. To now, the only treatment shown to be effective in clinical trials is an alternative procedure called a hematopoietic stem cell transplant (HSCT). But obstacles remain; the procedure has yet to be approved by the FDA despite being in trials for decades, so Katie has to travel to a clinic in Mexico for treatment costing around $50,000, none of which will be covered by insurance.

The Kelly family has started a Gofundme page with a goal of $60,000, a figure that would cover the procedure, travel expenses, and follow-up care. So far, crowdsourcing efforts have raised around half that amount, and the Kellys are hoping that a fundraiser planned for next Thursday, June 28, from 6 to 10 p.m. at Florian Hall on Hallett Street in Dorchester will help make up the difference.

The event will feature a silent auction, a raffle with prizes including tickets to “Hamilton” and Red Sox games, and a live performance from the Dorchester-based band The Fenian Sons. Ahead of the fundraiser, Katie expressed gratitude to her family, friends, students, and coworkers who have already given her so much support.

“I’m so fortunate that we live in a community where it’s such a tight-knit group that they all support each together,” she said. “I hope that if the procedure works well for me, that I’ll be able to share this story with other people who think there’s no hope. And maybe by getting the word out, it will help to get the procedure approved.”

Tickets to the fundraising event in support of Katie Kelly O’Donnell are $25. To purchase them go to Eventbrite.com/e/help-katie-fight-fight-ms-tickets-46122626016. For more information email Mary Kelly at mlk9647@comcast.net. You can donate to Katie’s Gofundme page here: gofundme.com/help-katie-fight-ms.