So sorry Vinegar, that sounds awful and I can't imagine having to see a loved one go through that.

One of the few things I know about lung cancer is that in the advanced stages breathing can become very erratic, so it can be normal, then fast and shallow, stop for a while, then start again.  This would presumably make a much younger person feel weak and limp never mind someone who is 88.  The not remembering could be a side effect of drugs she is being given? (I only say that because when I was last anaesthetised for an operation I kept dying and coming back again but I only remembered the bits where I was wide awake.)

Have you spoken to her medical team?  Maybe mucus is pooling in her throat making breathing harder than it need be?  There might be positions she could be moved into that she finds more comfortable?  I would be asking for anything they can do to make her more comfortable and make sure with your mum that she's happy with it during her more lucid moments.

I hope they make her comfortable and painfree and that when the time comes she is able to pass peacefully.  She is so blessed to have you with her.

Best wishes, LJxx