Your mother in law is a narcissist! She will not change. You have 2 choices.... give in and grin and bear it, and let it roll off your back, or assert yourself and push back. Invite her into your world of function and structure, set the rules. More than likely she is not big enough to handle it so she will retreat. More than likely it will be a distant relationship. Your partner's support in standing united with you is the best thing although I'm sure it is hard since it is his mother. There are plenty of books on the subject. My favorite is called Nasty People by Jay Carter. It's really validating! You can buy it at Barnes and Noble. Another is The Wizard of Oz and Other Narcissists. This one is on Amazon.com

Hang in there!