AAAAAAAAAAAAARGHHH! 
Ah, I feel slightly better already.
I know I am NBU, really I just want to hear that I am not alone and others also have a MIL who does the passive-aggressive, undermining, undercutting, things that are never enough individually to make a huge deal about but all put together are enough to make you feel that you'd prefer chewing aluminum foil to picking up the phone when she calls....
DH feels the same and has spent his whole life dealing with avoiding it, while watching from a safe distance the trouble she starts/stirs in other parts of the family. I am only a decade or so in, and still I end up with bite injuries on the side of my tongue when she phones. I hate people deliberately trying to create trouble when there is none.

Sorry, not really an AIBU, perhaps we need a "rant" section? 