Don't want to just read and not reply, though I have little advice to give.
If your situation has been anything like mine, you've waited so long 'for the end' that probably initially you just felt huge relief that for your mum her long suffering and journey were over. No idea if that's the case, as my mother is still here, but I imagine that will be my initial reaction.
My mother also hasn't spoken or reacted to my presence for 3 years now, but she is still there and I can visit.
Although I often refer to it as similar to visting someone's grave, she is still physically 'here', even if I lost her years ago. After the funeral you're probably now realising that even that 'last link' has gone.
I know having looked after my in-laws, living next door to us for the past 20 years and 'intensively' ( i e 6 regular visits a day, plus any extras of course), the biggest change was realising our lives were 'ours' again. To do what we wanted, when we wanted, without having to do military planning for any 'time off'. 4
Suddenly we realised we'd just become so used to the routine, we didn't know what we wanted to do. 'That 'empty gap' might be what you're feeling perhaps?
It's now been just over 6 months since m-i-l died,f-i-l died the previous year, and although we still have yet to clear the house, we only just feel we can start do this, without feelings of 'intruding'. Now I know they hadn't got dementia, just all the problems of being in their mid- 90s and my father dropped dead one morning very suddenly nearly 20 years ago., so I know how different it is to watch someone die very, very slowly from dementia.
I often don't recognise my mother either, if she's in a chair in the main loungs and have had to have her pointed out to me by the staff.
I do feel angry that dementia has blighted the last 10 years of my mother's life too. At least my m-i-l knew the significance of her grandson's weddings and knew what a great-grand-child was and even had a couple of holds, whereas my 'old mother' (i e pre-dementia) would have been overjoyed to see her grandsons get married, be introduced to their wives and see pictures / meet her great-grandchildren. but as she is incapable of knowing who anyone is, or even being aware of anybody in the room, she wasn't able to do any those things. I get very cross with this disease which robs a person of their 'uniqueness' and personality.
I'm sure talking will help and hopefully in time you will start to remember the woman your mum used to be and rejoice in her life.
I've recently had counselling to help me cope with the anticipatory grief and the stress caused by what I refer to as 'her many dress rehearsals for dying' over the past couple of years.