This is a great story, and your kindness shows to a random stranger on the internet so I want to commend you for that.
Adding to it, I want to share a bit of my story and some words that could help as well.
I haven't ever checked for Lyme diagnosis, but I've experienced symptoms that are diabetes adjacent and cured those through diet and other experimentation. Through the last 10 years of so I obsessed over and reversed various medical illnesses that were said to be incurable, since for that exact reason as you said "conventional options have been exhausted". In my journey I met one man who exhausted many treatment options for Lyme and his success strategy looked as follows: a) he took EMF seriously and rebuilt his home for EMF minimization (happy to share strategy and solutions for you more here, I follow a cheap mans version of his more expensive work), b) he would take particular vitamins and other nutrients, and c) Rife therapy. He had an expensive plasma machine that would send particular frequencies into his body through light plasma (more expensive Rife frequency modulation end of things) but many machines exist that are cheaper. Spooky sells these machines, some of the solutions include PEMF which I believe are electricity based. I've used their remote frequency machines and also a scalar version for overall health and haven't had to use them since. My experience with Rife is limited. My basic drivers for health now are grounding for inflammation reduction (feet on grass every so often, or grounding mats), EMF reduction, information management (try notification zero and how it affects your biology: no notifications on your phones or devices ever and that includes notification bubbles - Calls from loved ones OK), and diet/food/water/sleep. I'll also use a Schumann tuned set of tuning forks I have 2 sets one that use a weight vibration and another that uses just the sound. my sleep and stress improve considerably when I use the forks, and I believe they have an affect like grounding but on the frequency end only. When I was first starting this journey, I would do pure cold showers in winter months and kept the practice for years, it was the first time I noticed a big shift in my health and wellbeing that lasted and also kept my mood elevated for a while after. I have also used more expensive cold baths, cryotherapy, etc and I think they can all approach and work for the type of Hypothermia treatment that geekfeatures is mentioning. My intuition is experimentation with these first, 3-5x a week, would mimic a similar process in the body to the hypothermic heavy therapy and may even be triggering it at a similar level to the paid therapies.
Anyway I'll stop there to keep this limited in word count. Feel free to reach out here or personally via hello@mannan.is and good luck.