I started a thread ages ago and the responses were very helpful and did wonders for me really. In case anyone would like some background: here it is.
My issue now has narrowed a lot in focus. I'm basically at the stage where I have to consider cutting off my mother long-term. My last straw moment came today, when I was looking through our 2015 calendar so as to copy down the day to day events of the IVF I went through in March / April, as I'm due to have another round this spring, and I wanted to remind and prepare myself for it all. Long story short: last summer my mother cat-sat for us while we were away. We returned to find that she'd 'accidentally' 'spilled' boiling water on our calendar. Ok (I thought) these things happen. It was still usable, a bit damaged but hey. Just now I went to March and April to remind myself of the IVF schedule, only to find that those months had been glued together. No other months, just those. It was impossible to see anything I'd written. It sounds mad, but this is unsurprising coming from my mother, and I should have guessed at the time that it wasn't an innocent accident. She'd obviously decided that info about our IVF shouldn't be lying where 'anyone' can read it (despite the fact that only she would ever go through our stuff, none of our other guests would). So she glued the pages down and faked an accident. It was the only clear outline of our IVF treatment that I had 
In case this sounds like an implausible accusation I'm making, she has form for this - 'accidentally' spilling coffee on unsent letters I wrote as a teenager because she'd opened them and disapproved of what was in them. When I was 11 I came home from school to find her burning all my diaries. It's bringing it all back up for me.
She has Paranoid Personality Disorder (not officially diagnosed), but refuses to see this and refuses to do anything to help herself. She has lived with her mother (whom she hates) for the last ten years. She has never had a job or a proper relationship. I invited her up this Christmas, even though I knew it would mean walking on eggshells and lots of very triggering things in between. The first time she got me alone it was to tell me that her brothers want her to kill herself... We managed to get her to leave when she said she would (she'll often stall and try to stay for a month), but on New Year's Day I received horrible accusing texts from her about how I've made her look a fool and betrayed her. You'll see from my old thread the very serious things she's exposed me to - homelessness, for example - and the dreadfully damaging lies she told me about my dad.
Writing this, it seems screamingly obvious that I should cut her out, at least for a while. But when I do that (I've done it before for a few months each time), the guilt I feel is tremendous: all she has is me, she has no-one else and I do worry for her safety and health. But this situation cannot continue. Last year, just before the IVF, she turned up on the doorstep unannounced wanting to stay. I can easily see her doing that again. I have enough to deal with as it is; can I, in good conscience, go NC?
Please excuse all typos and errors!