I am also so scared about getting MS.. it is one of my worst fears.
My grandma who has since passed at the age of 65 had MS, and died from complications of it. She was diagnosed at the age of 30 and had it for more than half of her life. Luckily times have changed and the treatment is improving, so your friend has more options than my grandmother did if she is diagnosed with it. My grandma was able to walk for about ten years, then needed a walker, and for the last twenty she was in a wheelchair more often than not. She could walk with a walker but it took her a lot more time to get anywhere, so she generally rode in the wheelchair because it caused less pain. MS can also cause other symptoms and my grandmother was unlucky and got most of them, such as bladder problems, problems with eyesight (she had to wear very strong glasses most of the time, MS induced diabetes etc.
I hope that your friend does not have this diagnosis, or that if she does, she can manage it better than my grandmother could. I know what i'm sharing is very depressing, but that is the realistic picture of my grandmother's life with MS.