what can I do about his mother stealing and talking about me?

[Greg]

I live with my fiancee and when we are at work, his mother comes to the house and rearranges my kitchen, steals silverware, pot scrubbers, and dishes. She packs my belongings up and hides things from me. She types awful things about me on facebook and I am sick of this woman. What can I do? Her family just says overlook her she is an old woman, old woman or not I am not her family and I want some type of legal action taken on my behalf.

[Lost]

Change the locks. Tell him she is not to have acess to your home without you present or install a camera and then threaten charges