Of course I'll never know, because no-one else wanted to know. The general attitude being, well, she was old, she had dementia, then she died, and of course lots of people die in much more tragic circumstances.
It wasn't a normal dementia death, considering all the things she could still do a few days earlier, (which the staff in the hospital clearly did not believe).
I think she was still mentally and physically capable of hiding pills and then taking the lot, and knew she would eventually reach a stage when she wouldn't be able to do so, and did not want to reach that stage.
If someone habitually threatens suicide it is difficult to know when to take it seriously. And in theory I think she had a right to commit suicide if that is what she did.
Lila