This is what is so heartbreaking. When people get a serious diagnosis (i.e., althzeimers, dementia, cancer, etc.) it's the start of losing control of their own lives. Doctors will start to decide treatments with the patient's consent, but the patient is catapulted into a completely different life. Even consenting patients will feel out of control because of treatment routines, side effects, etc. Their world changes, they can't go back.
By coercing Rebecca to agree to the trial, Randall just adds to that level of helplessness and lack of control. It is absolutely heartbreaking. Rebecca should hold what level of independence and authority she has over her own life close and dear. And her family should be a support system and allow her to live her life and make decisions for herself while she can. They can make suggestions, be a sounding board, but please, give Rebecca the control and dignity she needs right now.
I'm not sure I described this well, but that's how I feel.
And by the way, there should have been a screen at the end of the show that read: "And this, fans, is why people should go to therapy."