Kelly Ann Alexander, 43, says horse Aliyana was the reason she felt compelled to go to the hospital to have tests.
She said after she began suffering seizures Aliyana started to sniff the right side of her head.
Kelly Ann went for tests which revealed a low-grade brain tumour.
Kelly Ann, from West Lothian, has spoken out ahead of Brain Tumour Awareness month in March, and is working with Brain Tumour Research to raise awareness.
'The best therapy I could ever have'
The former HGV driver said: "My horse is the best therapy I could have.
"She has adapted her behaviour to help me and, looking back, I now realise she was the first to make any sense to what was happening to me.''
Kelly Ann had just taken up her dream job as a groom in a professional yard in Aberdeenshire when she first became ill in October 2015.
Just weeks earlier she and Aliyana had completed in their first dressage competition together.
"Within days of the dressage competition, I had my first seizure and then was having up to 14 or 15 a day which were always preceded by a horrible metallic taste and smell.
"I was prescribed the anti-epilepsy drug Keppra, but was still backwards and forwards to the doctor.
"Kevin had been brilliant, but needed to get back to work, so I moved 200 miles back to be with my parents in West Lothian."
She added: "It was about five or six weeks before I next saw Aliyana, but when I did her reaction was incredible.
The tumour was growing
"She galloped over to me and immediately started to sniff the right side of my head where, as we now know, the tumour was growing."
Eventually, Kelly Ann was admitted to St John's Hospital in Livingston, where the oligodendroglioma brain tumour was diagnosed.
She underwent surgery but challenged the neurosurgeon when told she could be left unable to walk or talk, insisting that she needed to be strong enough to ride.
She added: "Since my surgery, I have suffered with left-sided weakness.
"But Aliyana amazingly has learnt that she now needs to walk on my left side, not on the right as she was used to.
"She has even worked out that if she wants a treat she needs to be near my left pocket," Kelly Ann joked.
She suffered a major setback following the operation, after contracting a serious infection.
The tumour came back
In 2017, a scan showed the tumour was back and she has undergone further treatment.
Kelly Ann is now working with the charity Brain Tumour Research to raise awareness.
Less than 20 per cent of those diagnosed with a brain tumour survive beyond five years compared with an average of 50 per cent across all cancers.
She said: "My bond with Aliyana made me focused on recovering as quickly as possible.
"Doctors told me I wouldn't be able to ride for a year, but I was actually back in the saddle after just seven months.
"I trusted Aliyana would look after me and although I felt a bit apprehensive at first, I have found she always seems to know when I am tired and works extra hard for me.
"She even knows when I am having a good day.
"It was a shock to discover that the tumour had reoccurred," Kelly Ann added.
"I underwent radiotherapy and then chemo, but the best therapy for me is being with Aliyana, even though I have to rely on friends to get me to the stables as I am not allowed to drive," she said.
"The uncertainty of my future makes it very difficult for my mental health. I am having to take things very slowly.
"Added to that, because I am not allowed to drive, I have to rely on friends giving me lifts, including to the stables.
"I am still trying to compete in dressage competitions but find it very difficult as I get brain fog and can't always remember my tests.
"To me that doesn't matter as the important thing is that I have made an effort to attend.
"I don't care if I win a rosette or not, because in my eyes I am a winner - I'm winning at life after being told I may not walk or talk again.
"I have good days and bad days, but when I am with my horse, I forget all about my health. Aliyana is my best therapy," she said.
"I'm determined to make the most of whatever the future holds for me and, with Kevin and my beloved horse, I know I can put on a brave face and make the best of every day."
Joe Woollcott, community fundraising manager at Brain Tumour Research for Scotland and N Ireland, said: "We are very grateful to Kelly Ann for helping to raise awareness.
"Kelly Ann's story reminds us that brain tumours are indiscriminate; they can affect anyone at any age.
"Brain tumours are the biggest cancer killer of children and adults under the age of 40 and yet historically just one per cent of the national spend on cancer research has been allocated to brain tumours.
"We cannot allow this desperate situation to continue," Joe added.
To donate to Kelly Ann's Gofundme page click here