It sounds like her grandmother's options here are, "Die sooner" and "Die later and be really miserable in the meantime, and also run the risk that the intervention is going to kill or not be effective." (The "not be effective" point seems to me to be important here- my understanding of ovarian cancer is that the prognosis is generally poor, even with optimal treatment, and this sounds like advanced disease.) Neither option is great, and there's no point in expecting or insisting that someone take the news well.