I am sorry that you experienced such a shocking MH crisis - you have done wonderfully to pull through. Your DCs and DD must be v relieved and v proud of you.
Have you been under any specific pressure recently and been aware that you are feeling especially vulnerable - or has this been the same intensity for the last 2/3 years?
Making assumptions on your age - excuse me if I am off - but if you are having monthly arguments - is it related to peri-menopausal PMT or other peri-mono issues (anxiety, irritability, insomnia)? I never ever had PMT until meno - then I had the RAGE.
Maybe a physical and MH check in with GP to ensure you are all in balance.
As PP has said - a stuck ptsd emotional flash back might be at play with intrusive thoughts.
She did say those cruel vicious words back then but she isn’t saying it now, again and again and again. You did exceptionally well to get some sort of action out of her even though it didn’t satisfy you. That’s a major achievement with anyone with a PD.
A 2 stage technique for dealing with intrusive thoughts is:
1: “Thought stopping” - literally visualise a big red STOP sign or the palm of your hand flat up against her face once those words / images / sensations float up. Or any image that works for you.
2: “Thought Substitution” Need to fill that mental space immediately with something v positive. A list of your top 3 wonderful attributes, a wonderful song, a beautiful memory.
Impressed that you moved away and with your DH for having your back - but don’t let her pollute your life and destroy your marriage and family from afar. You need to preserve that. I wouldn’t worry about her having minimal contact with your DCs - you have won already - she has missed out on so much time from their childhoods that she can’t ever make up. At your DCs ages they are not going to prioritise seeing distant GPs 6 hours away.
Look after yourself, you have been through a lot - see your GP, manage the ptsd intrusive thoughts, drop the stuff with your DH and give him a hug and all will be well.