The coating that protects nerves is damaged, which means vision can become blurred and it affects how you move, think and feel.
Capill, 50, was effectively blinded by the disease.
But now she can see words again.
She returned from Mexico on Monday, after taking a punt on invasive and high-risk chemotherapy and stem cell transplantation (HSCT) treatment at Clinica Ruiz to halt the progression of her MS.
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The HSCT treatment, which is not funded in New Zealand, is the only treatment known to halt the progression of MS.
For Capill, who was diagnosed with MS in 2009, the treatment was worth every penny of the $90,000 required to fund it.
"I lost all my hair because of the chemotherapy but I couldn't be happier," Capill said.
"My vision is slightly better, my brain fog has gone, and I intend to get the walker out in six weeks or so."
The four-week treatment harvested her stem cells, and replaced them after chemotherapy which wiped out her immune system.
"The treatment has halted the progression, but the doctors did say that the improvements could take up to a year," Capill said.
"The analogy they used was my body now has new recruits instead of an experienced army.
"My immunity will come back in six months, right now it is like a baby's."
She has nothing but praise for the doctors and nurses at the clinic.
"You would think 'it's Mexico, it might be dodgy' but it isn't.
"They are so amazing, they thought of everything. The treatment far exceeded my expectations.
"I remember the first day I went for an interview [to assess treatment suitability] the professor took my hand and said 'we will take care of you' and it was the first time I felt like I finally had hope."
For Capill the first few years of MS were bearable. She started off at a 3 out of 10 (walking) on the Expanded Disability Status Scale (EDSS).
But because she has progressive secondary MS, she was not eligible for drugs funded in New Zealand.
Before the treatment she was at a seven and a half on the EDSS (not walking) and was confined to a wheelchair.
"My brother came from Auckland to meet me and he said 'I cannot believe you look so well' even though I had no hair.
"The hope you get is amazing. You can't put a price on it."