Op what sort of relationship do you have with your son in law?
I wouldn’t normally recommend going behind your DD’s back but she sounds very unapproachable.
Could you appeal to him? Say you need more calm? Can he speak to her on your behalf?
If she is autistic then she is low on dopamine and my dd as a teen with ASD definitely used me as her verbal punch bag to relieve stress. I’m not saying I was the perfect mother always either but when she was wound up, she would seek me out and almost cause an argument to get that dopamine hit.
Could this be the case for your dd? That she had got in to the habit of using you as a punch bag to relieve her own significant stress if she has ASD?
The difference is that my dd grew out of this habit around the age of nineteen.
Whatever the issue is op, I would recommend not getting drawn in to the minutiae of arguments and start gaining a little control over when she visits so that you can relax in between times. You can’t live in a constant state of dread.
So when she starts the next upset say something like, “I hope you know that I love you very much but I can’t tolerate any more of these constant upsets. I have done my best to support you but it’s never enough. From now on, if you want to see me, you are very welcome but you need to give me advance warning of when you are coming and if you start causing an argument for no good reason, then I will be ending the conversation” and follow through op. Walk out the front door if you have to!
Tell her, “I have tried my best to be accommodating for many years but I think the time has come when you need to look to yourself to solve any issues you may be having.”
I think sometimes, after a certain point, we do more harm than good by pussy footing around.
Of course the above only applies if you genuinely feel that there are no major unresolved issues between you and that she doesn’t have legitimate cause for complaint.