AIBU to consider cutting contact with my difficult elderly mother?

She has a BF and friends, I would just stop taking her out for lunches, stop messaging via text and focus on your family. Sounds like you'll never get her approval so why bother trying. Also, stop telling her what you are doing socially as this invites opinions!

Limit contact to a phone call/visit and hang up/walk out as soon as she kicks off. DH had to do similar with his Mother as she went through a really nasty phase in the earlier stages of dementia. It was like training a puppy with Gravy Bones, if she behaved she got his company otherwise he got up and walked out and tried again a few weeks later.

I suggest you tell her that you can’t go on with her this way, that things need to change. Try to lay some ground rules. Maybe her GP would give her some counselling sessions. If you make it clear that you are so unhappy you are not sure how to keep going with her at all, she may be able to contemplate change.
she clearly isn’t a mature well balanced individual and probably needs things to be spelled out for her, boundaries to be crystal clear.

"call me a liar. Insults and accusations of neglecting her then follow."

"She will say I am unlovable, cruel, neglectful, a selfish sod."

" she says I’m a cruel, neglectful daughter and all her friends think I’m horrible."

I'm so sorry you're going through this OP. She is being abusive to you. You don't don't deserve to be treated like this and don't have to put up with it because she's your mum, it's ok to cut contact. Think about what you'd suggest to a friend if it was their partner saying these things. I think you need to go no contact to protect your health as you say it's making you depressed (which is very understandable). Her behaviour has led you to get to this point, sadly you can't change how she behaves. If you go no contact she has brought it on her self.

If my OH had a sister, I would swear you were she! His Mum is very much the same. I regularly suggest he just tells her to do one but he is much nicer than me. We have reached a point where he does now have stock phrases ‘I don’t recognise this version of events. Sorry, but I’m putting the phone down now, Mum.’ which she hates but which has meant we have had less nonsense. I basically draw a line at it affecting our family life so he has had to make some decisions about boundaries. Luckily she can’t come to us - her rocking up must be tricky.

If she bitches about money you could always say “well mother you burnt through inheritance, and are leaving me with nothing so time to cut your cloth! I cannot afford to pay for you every time.”

Could you just not engage when the inevitable disagreement arises every so often? So when she asks why she's not invited to your birthday dinner - you say 'I wanted time with just DH'. If she makes the predictable neglectful daughter/you're being horrible comments just don't entertain them - 'I can see you're being nasty/silly/unreasonable again Mum. Give me a call when you're in a better frame of mind'. And end the communication.

Well of course it is getting worse because you do eventually give into her and agree to not talk about it.

My advice would be to make sure you do talk about it. If she has a tantrum and won’t talk about it then immediately stop talking to her. Depending on where you are tell her to go away or you go away. I would advise LC rather than NC.
I had a similar, but the not the same, situation with my mother. The difference is that I have a sister who feels exactly the same as me. My mother is now in a nursing home and I phone her every week but neither of us have anything to say. I visit a couple of times a year.

I personally would stay in contact in some form but I would accept that she probably has a personality disorder and try to detach emotionally.

Behaving like this to her child is deeply dysfunctional. Tbh do you think these ‘friends’ really exist? I doubt it, or at least I doubt that they say anything at all about you. Possibly they make vague agreeing noises when she says stuff to them, and she translates that into whatever she feels like.

Work out what sort of outing or visit with her is least stressful and do that. Maybe visit her at home so that you can get up and leave calmly when she is horrible to you ‘I’ll see you when you’re feeling better mum’.

We both know there’s no point trying to deal with this sensibly or healthily cos she won’t engage.

Has DM always been this unpleasant? If not, she’s got the early stages of Dementia which are oh so hilariously referred to as personality change.

You might have to go low contact because you need all the peace you’ve got before she gets worse and the crisis years start.

If she has form for being a wicked old trout, Go low contact and stay there.

My recommendation is that you cut off all contact. You have been a lovely and very patient daughter and she not only takes you for granted, she is actively cruel and unpleasant. Your sibling who does nothing for her is the 'golden child' while you are the 'scapegoat' despite you doing everything for your mother.

Think how peaceful you life will be without her toxic and entitled behaviour. Your sibling can step up once you pull right back. It's their turn now and it's long overdue.

Why do you just blindly pay for her and do these things though? The second someone took it for granted that I would pay their way to the point of being rude about it, I would stop

Ditch the bitch.

The way out of this is to stop doing what you're doing. She's ungrateful and abusive. You don't have to put up with being treated like that just because you happen to be related. Would you put up with that treatment from anyone else?

If you're worried about how she will manage getting older, you can ask for a referral to adult social care when it's needed. At the moment, she's perfectly capable of taking care of herself so you don't have to worry about her.

And if she tells her friends that you're horrible and they think badly of you, so what? They're probably more aware of her personality traits than you think, and probably find her difficult too. You can't live your life worrying about what other people think of you - you know the truth and it's your opinion that matters.

I'd limit contact, cut the call or walk away whenever she starts being abusive.
To be blunt, she will likely die in the next decade. How will you feel if that happens and you're no contact with her? If you think you will feel relieved, go ahead and cut contact. If you think you will feel guilt and regret, continue to be in contact but on your terms and be firm with boundaries.