I wanted to ask, if it was legal, would you euthanise her?
Spooky - I'd written my reply to tap before I saw you'd posted this!
The answer is yes, I would.
She has no real quality of life left to her now. The vast majority of the time she is scared and miserable and confused, its very rare that she is happy. She cannot enjoy any of the things that she once loved - crosswords, jigsaws, she cannot even follow a TV show (she thinks it is all real and happening outside a window). She wants her mummy and daddy all the time, gone some 40 or 50 years ago. I'm crying now.
I honestly and truly believe that if the woman she once was could see the woman she is now, she would agree with me. She wouldn't want to carry on in misery. Its not so much the physical aspects as the mental - she's not living, she is existing. A lot of the time she is actively miserable. A lot of the time she is simply vacant. Very very rarely there is a flash of happiness.
So yes - I would.
From an atheist/humanist perspective.....this is The One Life We All Have, and while most of the time I would say "well, things might get better - let's hang on one more day and see what happens", there is NO prospect of that happening. She will only get worse, and more unhappy, as time goes on. There IS no life left that she leads.
And from a theist point of view? If I end her life, she will be reunited with her parents and her husband and her daughter. No more misery, no more fear, and her brain will be restored. In her circumstances, I cannot see any reason why a believer would not stand right behind me on this one. And frankly, there is no loving god who would not likewise be saying to me "yes - that is the right thing to do".
So yes - I would.