I think the first step is by not jumping into another relationship unlike *ahem* others I know.
I personally think it's all in how you are raised.. I know for a fact that her mom manipulates the crap out of everyone including her H. She's grown up with it. She's also got some issues physically that are a result of her being born WAY premature. So.. she's always been sheltered. I mean VERY sheltered.
Her mom is the main source of her self esteem. I kid you not.. that woman will walk into the house and say these 3 things before she gets her coat off:
1. Have you gained weight? 2. When's the last time you vaccuumed? 3. Have the girls eaten?
She attacks the 3 things my wife values most:
1. Her self image 2. Her housework (she is OCD in this department.. no kidding) 3. How she's raising her children.
10 minutes and she's depressed as all get out.
She also mind jobs you. If she watches the girls.. or helps you out in any way, she gets the opportunity to play with your head.
I've tried for YEARS to get W to see and understand this. She had made some progress, but unfortunately, she viewed me in the same light. She really is in dire need of counseling. I'm very scared at how her way of being is going to affect the girls. When we were together, I could shield the girls from this. Now.. it's wide open.
Just a quick aside to how messed up MIL is. For our oldest D's 1st B-day, we had a party at our house. We had the cake and everything. Instead of waiting for W and I to give D the piece of cake and sing Happy B-day, she took it upon herself to start.
I yelled at her.. wrongly.. in front of everyone. "What are you doing?? Let W do that!!" It was after all our 1st childs 1st B-day.
I got hell for 6 months.. I eventually had to apologize to MIL.