Here is my 2 cents ...
I am giving MIL the benefit of the doubt re: age / hormones / medication / chronic pain , etc . Let's say for one moment that she isn't really trying to manipulate or cause drama .
Let's say that she gets in some funky paranoid panic attack where she gets hypersensitive and is convinced that everyone secretly hates her and suddenly , little incidents become " proof " that her suspicions are correct .
I would print her out a card ( like a 5x7 or 8x10 ) that says something long the lines of this :
We love you because ____________. List a bunch of things .
We want you in our lives because ___________ . List a bunch of things .
We would never deliberately hurt you by ___________ List a bunch of things .
When you feel unhappy , read this card and know that these things are true .
Give it to her and talk about it . Let her know the card is for her to use when she is doubt or is feeling unloved . If the drama persists , cut her off the the words " MIL , read the card we gave you . There is nothing more we can do to reassure you ."
It's kind of like dealing with a toddler , but it might just work .