What if she wasn’t physically healthy? Water on the brain causes dementia like symptoms...It was not about saving her life, it was about improving quality of life ... at the age of 93.
How severe is the dementia?
If she’s capable of understanding what’s going on around her, I’d do it if I could.
If not, I’d probably do what I could to keep her comfortable and let her go, but do nothing to “hurry it along”.