What causes people with Multiple Sclerosis to get Leukemia as well?


My mom has been living with MS for the past four years. The doctors keep prescribing her medications that are supposed to be helping her with the pain, progression of the disease, and some of the symptoms. However, so far each medication has caused something to go wrong with her body. Such as one of the shots she was on was destroying her liver and kidneys, and now some of the procedures that they have done on her have caused her to develop Leukemia. I don’t understand why this is happening. What is causing all these things to go wrong with her?
If you have any information please share it with me because we need all the help we can get.
I don’t want to lose my mom she’s the only person I have left.