South Beach diet for a 65 year old women with many medical problems?

I am not 65 but my grandma is and my aunt wants her to go on the south beach diet with her. She is not only 65 but has heart problems, Lupus, and recently got over cervical cancer (thank god). My mom, other aunt, and myself are strictly against it and we want her to see a nutritionist or her doctor if she wants to eat healthy. Does everyone agree with me that she shouldn't go on it?? Or do you think she should?

Thanks :]