What should i do about my mother in law?

I have been married to her son for 2 yrs now but together for 4 years. It seems that every time i turn around his mother and i disagree on something and he gets stuck in the middle. This last arguement i told her that bi-poler is hereditary and she did not believe me. And then all of a sudden she asks me if she should just have me commited if i think im bi-poler. She is supposed to be a christian to so what should i do to keep my pride but not hurt my husband?