..... was given a sedative in her coffee and had to be restrained by her husband and daughter as the doctor injected her with the deadly drugs....
Have now read that line numerous times. Doubting it can be true
Absolutely plausible. If someone is about to be killed, a sedative will do nothing. They will be alert and in survival mode. Also dementia is episodic. It is quite possible she didn't have dementia at that point but was lucid. The stress of someone trying to kill you can exacerbate dementia or trigger clinical anxiety and dementia or it could do the opposite.
If people want to die, I have absolutely no problem. I have seen that myself and there is no need to have a "doctor" with a syringe or a signed document or anything else. It is a natural process, not voluntary but not involuntary either.