*Catholic followers advice on disease please!!?

My mother was diagnosed with Multiple Sclerosis about twenty years ago. I, myself, am only 14 years old. I often hear her saying when she is having troubles with her disease, "Why is God punishing me?" Really she just says it to herself and not in a question intended to be answered by another. When I think about it I think about always keeping that positive attitude and beleving something good would come out of it. Although I do have to question myself. Is he punishing my Mom? What did she do that was so horrible? What will come out of this? I help my mom sooooo much it is sometimes unreal. Sometimes I think that's why I was put on this earth...(one of the many reasons) was to possibly be here to support her and help her as my father did not as they are divorced. Why do you think God is doing this? Thanks soo much!!