To not visit my MIL often after her dementia has taken hold

[Minusone]

Pre dementia My MIL was openly hostile to me, said she would cut my husband from her will to avoid me getting “any of her money” said it was a good thing when I had a miscarriage amongst other nasty things, these are just examples to give you a flavour of the woman. She’s now got dementia and I’m suddenly her favourite , she forgets who my husband is and always asks for me, on the rare occasion I’ve visited she’s delighted to see me, husband and sister in law have asked me to visit more often as care home staff say she’s so much more lucid after I visit, aibu to say no? Part of me wants to be the bigger person but the main part remembers the woman despised me and made my life difficult from when I was a teenager. My children won’t have a relationship with her because of how she spoke about me. Am I being unreasonable not to visit her unless it’s super convenient and I’m literally passing her care home with my husband?

Well, the brain changes from age, disease or injury and so the personality changes. I voted YANBU but she’s literally not the person that she was before.

Would you visit if she’d been lovely before but was now horrible? I don’t know the answer but if you can think of her as the different person and can find her company tolerable for short periods then I’d say to go. Regard it as both a kindness and a scientific experiment to see what different opinions she has now.

I don’t visit my FIL for similar reasons. My DH visits and arranges his care etc out of filial duty. FIL is not an easy man, and it is hard to tell which of his unreasonable behaviour is the illness and which is his personality. It is hard for DH who has never had an easy relationship with him, and I will provide emotional and practical support for DH, but I prefer it he can offload onto his siblings rather than me.
The DC have no relationship with FIL as he has never shown any interest in them.

Just wait until her dementia gets worse, she’ll be a complete bitch to you again.

Just because she’s been mildly half decent to you now doesn’t wipe the slate clean, and nor should you have to be the ‘bigger person’.
I hate that bloody phrase.
She’s had carte blanche to treat you dreadfully throughout your marriage, but the onus is on you to take it on the chin. ‘To keep the peace’, i’m sure?

My fil has dementia and i really hate visiting him. If i can swerve it, i will.

Yes, go more. Support DH and SIL. Be the bigger person here.

However, you can afford to be generous. A dreadful debilitating illness be grateful and hope her attitude continues to the end..