I echo all Granny G has said.
It is very difficult to deal with someone who has been and still can be so critical to you. I also understand the feelings of guilt if I don't visit, as mum would only see the carers if I didn't go too, but I do feel it important to look after myself first as yes ok mum wouldn't get visits from the invisibles but atleast she is being visited and cared for. I go once a week to visit and phone between times.
My thoughts only - maybe its time for you to a have break from visiting to recharge your batteries, then when you are ready to start revisiting, worry about battles that really matter to you, and not ones that in the great scheme of things, after taking a step back, are not really important. In my opinion, it is important that I look after my self first and if the situation get so bad with mum, I take a step back and leave it to the carers - it doesn't get rid of the guilt monster, but it does give me a chance to be a better carer for mum.
Oh it's so difficult isn't it. Thinking of you
Ps I meant to mention that when mum was first diagnosed and a bit before, mums critical behaviour got even worse, it was as if her usual nasty behaviour was heightened and I was convinced she was just being a b 1 tch just to do her upmost to upset me...... But this has now passed. She still occasionally "tries" to one up me, but now it doesn't affect me, can't give you any blinding flash of inspiration on why it doesn't, it just doesn't. If I feel a twinge of hurt I just walk away for a bit and when I walk back, start again as if nothing was said.