It depends what you mean by suffer.
I think mum herself suffered most at about the time I suddenly realised that she had dementia. She realised that something was wrong, but could not work out what and her confabulations (false memories) were all about people doing terrible things to her. She was scared and anxious, but fought everything tooth and nail - she would not see her doctor, or have carers in, allow anything that might have assisted her and half the time she wouldnt even let me in her home as she was sure I was stealing from her. It was an unspeakably awful time for both of us.
Once she moved into her care home, though, her paranoia disappeared and her old personality returned (although not her memory, obviously) and she became fun to be around, I got to know the staff and other residents and I would join in the activities or take mum out of the care home for little trips for coffee and cake, to go shopping, the local village fete, garden centres or pushed her wheelchair along by the sea, the harbour, or the park. Physically, she declined a lot during this time, but she was in her own little bubble and I really dont think that she was aware of her own decline. Even her last year, which was a bit of a roller coaster for me, did not seem to affect her. She very quickly forgot that she had been ill or had been in hospital. She was happy and content right up to the time she passed away.
Obviously, this is my mums story and your grandmother might not be the same, but it is likely that your grandmothers perception of her situation will not be the same as yours.
