I'm sorry, but a mil isn't automatically a friend...isn't a relative....she's just someone you get stuck with!
And a lot of the time she's insanely jealous that you've taken her baby boy away from her.
So though I empathise with mums who will one day be MIL's for their DS's wives, I am within my rights, as the OP is within hers, to dislike my MIL intensely!
She can't be civil with her own daughter, she has slagged her off in front of me and to me on many occasions, so I can imagine what she must say about her DIL!
She is a complete curtain twitcher, absorbed with other peoples lives, and spends her life thinking that other people are 'looking at her funny'. Her negativity can suck the life out of anyone's world and one day a week, I inflict this on my DD because I don't want to deprive her of a grandparental experience (my mum lives too far away and has so many grandchildren she doesn't make so much fuss of dd).
Luckily DD is young enough to ignore the behaviour she doesn't like...and has (so far) not repeated any of it. DD is just getting to the stage where she thinks nanny is 'mad' and has stopped asking if she can stay over.
Sorry for the rant, but my MIL drives me nuts....and I'm usually quite placid.