Oh dear. That sounds like a very difficult situation for you both
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Going back to your original question, who is looking for permission to die? You or your mother? And at what level of authority would you or your mother accept that permission if it was given? I mean, if I gave you permission would that be enough? I sincerely hope not since I am in no position to make any sort of judgement, let alone give you that permission.
I think you either need to talk to a doctor whom you respect and/or a religious authority from whatever faith you follow (whom you respect), or perhaps a counsellor as an alternative. It doesn't sound to me like you would benefit from someone who is going to lecture you on the what is sin and what isn't so try to find someone with a sensitive and compassionate attitude.
What I would recommend is a book called "Love, Medicine and Miracles" by Bernie Siegel. It is written by a cancer specialist but is very worthwhile reading for those dealing with any sort of severe illness/accident. IMHO. If you can't find one (try magrudys or booksplus), PM me. I can leave one at the second-hand bookshop in Jumeirah (when I remember the name) for you.
Voya con dios.