Is it true that chemotherapy makes it worse when you have sarcoma cancer?

My cousin was diagnozed with the intestine cancer (I was told it was an uterine at first) a few weeks ago. The cancer has already spread to her lungs, kidneys and everywhere else. She had a surgery and they removed lots of it from the different parts of her body. She felt better but then the doctors run some tests and found out that it was a sarcoma type. I know that the sarcoma resists to the chemo therapy treatments but is it true that it might make it worse? I never heard of it but the doctor says that there is a chance that the chemo will make more damage than good. She was asking my mom whether she should go for chemo. Does anyone have any experience with sarcoma in such a late stage? What should we expect? What will happen next? And did someone at her situation lived for long? Is she going to experience a lot of pain? It's hard for me to ask these questions her doctor because she is in Europe and I get all information on the phone only. I am scared.