I'd just like to welcome you to the forum, and so sorry to read of your Mum's situation. It is so hard and painful to witness a loved one gradually decline. I had the same with my Mum, and I had the same thoughts as you at times.... I just wanted her to be free of this horrible disease and be at peace. So please don't feel ashamed or guilty of such thoughts. Its natural. We don't want to see out loved ones suffer.Hi.
I joined this forum for exactly this reason. I feel like I am already grieving for my Mum who is physically still with us but to all intents and purposes, is actually 'gone'. I am struggling with such a huge range of emotions and thoughts right now, some of which I actually feel quite ashamed of. (i.e. it would be better for everyone if Mum passed away) - really hate myself for thinking this but I know she is now in the condition she absolutely dreaded and expressed as much when she was aware enough.
Wishing you continued strength at this painful time.