M.M.
When I read the title of your message, I just had to laugh-out-loud. Who doesn't have problems with their mil? :o)
Mine isn't mean or anything, she is just always in our business and extremely opinionated. I've learned over the years that calling her on her stuff and setting firm boundaries in regards to my/my husband's personal life and how I choose to raise my children has helped ALOT.
And when she gets really bad....I just drop a reminder that I hold the key to her seeing her grandchildren. That gets her in line real quick.
I try to be a little sympathetic to her though sometimes...I mean, I am extremely bonded to my son and when/if he marries..it will be hard to let him go and move on with another woman in his life, you know? But I also know the person I am, and I am always concious of others feelings. I think sometimes mil's can be very insenstive...and they forget what it was like when you become a mom for the first time and are figuring things out.
Try setting some firm boundaries. Don't be afraid to let her know when she hurts your feelings, steps on your toes, says something to offend you. Because really, it is WE who are responsible for how others treat us. Unless you let them know they are doing wrong, they might never know it or even think it is okay to walk all over you.
Keep your head up...I guess I'm lucky my mil lives thirteen hours away! :o)