Ethical dilemma but yes I agree. If she can’t understand what the medication is for and that she is dangerously underweight, it’s not informed consent/refusal. Also being starving and dehydrated is not really helping the brain function either. From the comments it doesn’t sound like she is ready for palliative care, doesn’t want to die. So her wishes would be better met by giving her the medication. Perhaps giving sneaky doses for a week or so and see what happens. Reassess if she starts to regain some decision making capacity.