I am trying to get my head around this.
A bit of background - fairly average family, one sister 10 yrs older than me. Happy parents with ups and downs, good lifestyle, both treaded very similarly and fairy. No one neglected or over indulged. I am now 50 yrs old.
My father passed away 10 years ago, quite suddenly. My sister's behaviour became terrifying and manipulative, during those first few years she took over my mother's life entirely, from finance to care. My mother did not resist as was very depressed and never recovered from the loss of my father. I calmly tried to discuss this with both of them at the time but it was impossible. It was heartbreaking for me to watch my mother succumb to this as there was no history of anything quite like it in our lives.
After several years I had to walk away. My sister was abusing my mother daily, screaming in her face, checking her bins for what she had bought or thrown away, taking control of her home and sacking a gardener my mother needed. I sought counselling to deal with it and was told to notify social services. When my mother went into hospital with an infection I was informed that she was mentally sound so nothing could be done about my sister's abuse unless she reported it. None of this was physical abuse, to my knowledge. I had to watch this for years feeling helpless, whilst my sister drove me out of the way, even hiding my parent's will and blocking all phones.
The abuse involved cutting mum off from friends, dragging her to places she didnt want to go, screaming and shouting in public at her and humiliating her. I was so scared for my mum's safety that I almost shut down inside.
Eventually my mother passed away during the pandemic, I was living at a distance at that time, so the house sale was dealt with by solicitors and split between myself and my sister. We didn't have to meet.
Fast forward to 2021 my sister contacts me, seemingly a calm and friendly person, saying our mother had left a smallish cash inheritance she had in her account and wanted to give me my half. I very, very tentatively resumed contact, it was nice enough, and I think the death of my mother had numbed me to the trauma of the past.
Since then, I regret this.
It took her until last June to actually send the inheritance to my account. There was always an excuse, passed off with a giggle or faux ditziness. Then she moved to texting me morning till night, utterly dominating my time with senseless questions, ploughing through boundaries and then buying me expensive gifts when she realised I was pulling away. To cut a long and tedious story shorter, she told me this Xmas that my mother had left a box of letters addressed to me, stipulating that I was to receive them when she passed. These had been written from my childhood to her old age. I asked her why she had never given to me in the past 3 years we have been in contact and she changed the subject, but with utterly no shame, declared that she had read them all and that she would bring them when she thought it was 'appropriate' 
My Dh has hit the roof. Our surviving older relative was also told this and said her jaw dropped to the floor. I am certain that no contact is the only sensible option now, as the past few years have been a tremendous drain, but...
HOW the hell do I process the trauma of the memories that have returned that were numbed? All of the pain and horror of watching her hurt my mother, telling terrible lies (about cancer, work colleagues, etc)? Hearing about the letters was like a thunderbolt that cracked open my memories of her abuse, my body is so shaken. I am happy to pay for some therapy, but in the meantime I would so appreciate some pointers as how to safely get her out of my life.