@ellesee It is would probably be more correct to say that your friend has a higher risk, as opposed to a high risk. There is a significant difference between these two categories. And if her mother does not actually have Multiple Sclerosis she may not be at any increased risk of having the illness herself.
To quote the Mayo Clinic website:
The risk of multiple sclerosis is higher for people who have a family history of the disease. For example, if one of your parents or siblings has had multiple sclerosis, you have a 1 to 3 percent chance of developing the disease — as compared with the risk in the general population, which is just a tenth of 1 percent.
you can see that the risk is still very low