Lying about being pregnant?

I am 31 weeks pregnant and I live with my fiancé and his parents. (We are desperately trying to find a home for ourselves) and all my "future mother in law" is saying to my fiancé is that IM LYING ABOUT BEING PREGNANT. How is this possible? I have had scans, tests, 3D scans, a gender reveal party, I have a huge bump... And she is telling everyone I am lying! How do I deal with this as this is clearly something she has against me personally?