Pied - I very much doubt they would put the pressure sore as a cause of death as its a consequence of her being in bed rather than a direct cause. I do appreciate you feeling the changing of the dressing and pressure area care may be superfluous but I think I understand why the nurses are doing it. If a pressure sore becomes bad and painful, because its a break down of the tissue it is affecting nerve endings, blood supply to the area may be reduced and it can become very painful and there is the risk it could become infected. If it seemed likely that your Mum was obviously hours from death then yes, you would leave it but if it gets bad, that will cause your Mum to become restless and although she may be aware of pain, or maybe a more intense irritation is better description than pain, she will want to move off it and maybe be unable to do so. Well managed pressure care, moving and half rolling and using pillows to support her as its done will mean maybe some discomfort for a short time as opposed to a niggling irritating pain that will continue to disturb her to an increasing degree.
Maybe you could ask the nurses if she could have a small amount of morphine before hand, perhaps you or sis could sit on the side she is turned to and hold her hand and talk to her whilst the care is being given. Be honest and say "its going to be a bit uncomfy for a little while Mum but if they do this then you will be able to get more comfortable after and relax and it won't be sore so you can sleep if you want to". Do they have pillows or wedges between her knees or under her feet that will change slightly the angle of pressure? and relieve it a little?
Do you have any music playing in the room? sometimes gentle music in the background can improve the atmosphere overall, maybe something light and classical or the type of music like the link earlier. Is there anything with a nice fragrance in the room? That can be soothing and could be a nice scented candle if allowed or a good quality natural room spray or essential oils? If you stick to the same fragrance that your Mum smells when she is awake she will associate it with you and the room and it will help orientate her. Maybe the lavender would be all you need.
Oh Pied - wish I could help more, we all do I am sure...
Take good care of yourself and gentle hugs to you all,
Love
Celia
xx
Its so hard because you must feel so helpless because you don't know if its for the best or not - but, as said, I do think I understand why they are doing this.