MS. On Three Day Treatment Of Steroids To Treat Severe Leg Cramps. History Of Having Burdock Which Is Advised Against By Doctor. Any Insight?

My sister has MS and has been given a three day treatment of steroids to treat severe leg cramps. I used to live in Japan where they have the healthiest diet in the world, and the highest number of centenarians. During my time there, I was married to a Japanese man who cooked everyday, and part of our meals was a side dish of burdock, a very popular and common vegetable root in Japan-- it is one of the strongest blood cleansers and an immune system booster. I also remember any time I had any pain or felt ill, I would immediately eat burdock along with aloe--another food staple in the Japanese diet, and they both worked beautifully to ease the symptoms immediately. Question is, my sister took burdock one day prior to receiving the steroid treatments and she said she slept beautifully for the first time in a long time, but that she did wake up as usual with pain in her leg, but it was only in an isolated small area and not all over her body as it was prior to having burdock.
However, later that day she was given her first steroid treatments, and the next day she had her usual painful attack of pain throughout her body. So she contacted her doctor and told him she was taking burdock (pureed from the natural root vegetable purchased from a Japanese market) and he ordered her to stop taking it as it was interfering with the steroid treatments. Is this true? If so, I am confused, because burdock is simply a root vegetable, like carrots, which is a staple of the Japanese diet--a nation of people who have one of the most highly praised diets in the world--and I myself ate burdock, the root vegetable, as a side dish everyday for two years while I was in Japan and felt nothing but fantastic and my skin also never looked so good. So why should it be working opposite to it's miraculous self in her body????? As a side not, If my sister were living in Japan and had such a similar question for a doctor in Japan, I am sure he would be shocked. But then again, multiple sclerosis is virtually unheard of in that country. Thanks in advance for any insight into this perplexing matter:)