... I reckon I'd have to hear what the woman herself feels about it. No one else can judge whether or not her life is worth living.
With severe brain damage existential questions would be difficult to comprehend. Should the doctors keep her alive because she is scared of dying but dont really understand the concept of death when they reach the conclusion her suffering is unbearable?
European Convention on Human Rights
Article 3 - Prohibition of torture
No one shall be subjected to torture or to inhuman or degrading treatment or punishment.
In my opinion its torture, inhuman and degrading to keep a human alive in that condition.
Living like that would be a nightmare, and non of you would want to continue live like that for decades. Most important would be estimate her quality of life, if keeping her alive is dignified living and reach conclusion if her suffering is unbearable . The rational in major of these situations is euthanasia.
Time must pass slowly for her when she cant engage in many activities that brings human happiness.
How will her life be when her parents die? Lie in bed 24/7 and stare at wall for 20 years alone in a nursing home without love? It will not be easier for her to get euthanized after the death of her parents.