My MIL was terminally ill with bone and lung cancer and we (her son and I) lived o/s.
MIL sent a letter (we used to write a newsy letter to each other each week) saying what an awful person I was for sending SIL a rude and unpleasant email, how could I do that to her daughter, how she was disappointed in me, how I had upset SIL so much etc.
I immediately called MIL and asked what email and had she read it for herself as I hadn't emailed SIL since the previous March (this was in October) and I would like a copy of it to read and establish how this could have looked like it came from me.
Apparently it was so awful that SIL deleted it without showing MIL, rushed over crying to MIL's and MIL took her word that it was true.
''why would she lie about that''? I was told.
I ended up in tears on the phone as there was nothing I could say that could convince MIL that I hadn't emailed SIL in the months leading up to that day. Eventually, I hung up and showed DH the letter when he got home.
From memory he flew in to see her, MIL had moved into SIL's home as her health deteriorated further and at no time was he left alone with his Mum to discuss what had happened. She was absolutely convinced that I had sent that email and nothing could convince her otherwise.
Over the coming months, when DH had returned home, the telephone line to the house was continued engaged so he couldn't speak to his mum and she died early the following year. She remained very coherent up until the final days.
SIL helped herself to her bank account (I have mentioned this in another thread) for a month after MIL died and now cousins and a remaining Aunty have all been told similar stories about me.
For the life of me I have never understood the desperation of my SIL to do something like that, so close to MIL's life ending. What did she benefit from that? DH always told me to be careful of her, but I took her as I found her. I doubt I will get understanding or closure on that period of time and goings on and apart from one or two members of DH's family, we have nothing to do with any of them now.