How do we get mom to take her medication?

My mom has lung cancer and is on a targeted medication that is working well. However, she refuses to take prescribed meds for the side effects of her cancer drug. She has always wanted people to feel sorry for her and it seems that she wants to have nausea and diarrhea so we will pity her. She just will not take the medicines to make her feel better and she makes a show of running to the bathroom. She lives with my brother and his family in another state, and we have all tried to explain why she needs to take the medicines (loss of electrolytes, dehydration, weakness, etc.). Does anyone have any suggestions as what we can do? My lovely sister-in-law takes her to her Dr. appointments.