Evil Mother in Laws

Throughout history there have been marriages, or at least relationships, in abundance. And where ever there is a relationship there is usually a mother. And a mother-in-law.
You know what they're like - with a few exceptions they're all nice to start with, happy to meet you and tell you how they like your style or how good it is that their son has found you.
Then comes the hard part. Either secretly or in open defiance of anyone being perfect enough for their child - they begin to manipulate you and your partner.

The first few times it may not seem like your mother in law is controlling. You were too busy and she didn't want to bother you with a decision. Or she was going to ask you to do it but it was quicker to do it herself. She says she's upset that you'd already made plans on the day she was going to have her birthday dinner - but that's alright, go out and don't worry about her!
Don't be surprised if it feels like she's secretly controlling everything. She probably is - maybe without even realizing it.

Great question! And I haven't figured it all out myself yet, either!
The old adage of Distance makes the heart grows fonder is particularly applicable when it comes to mother in laws. The further away they are the happier the relationship!
The most important things to remember:

1. It's your life and your family. If you have to offend her because you do things a certain way then you'll have to offend her.
2. Your partner needs to take your side. You and your partner are a family, and your family comes first above outside family members.
3. Take it in small doses. Set a certain time she can visit - even if that means lying about going out or banning drop in visits.

Next time your mother in law blatantly goes over your head or ignores you or does something childish and arrogant - treat her like a child. You might be surprised at the result.
If you talk slowly and firmly to her as well as repeat yourself ad nauseum, not only will she feel that she's not overpowering you - she might just get a bit of a shock at how she's being treated and even stop the behaviour.

I've been there. I'm still doing that (dealing with a mother in law, that is!) Hopefully you'll eventually come to terms with your own mother in law and even develop a relationship with her. If not, that's fine too. 
Just remember - she doesn't rule your life. Be firm. Be tough. Your own family comes first.

When I first met my mother in law to be at 18, I thought she was great. She was accepting, did everything around the house, didn't bat an eyelid at the fact her son slept with me in her house and was, in my opinion, totally cool.
After I'd been with her son six months I moved into a house with her and her daughter. Don't ever do it! I learnt the hard way that everything had to be done her way - and she was nice to you - as long as you did what she wanted.
My husband had already agreed to pay her and his sister's way through university so we were stuck there while he stayed loyal to her.
We broke up for awhile because of her - I got sick of the way she controlled everything - including not talking to her youngest daughter because she married an older man.
Currently she lives on the other side of the country... but she'll be coming back in six months... scary! Wish me luck!