Crazy bitch

I worked for my grandparents helping manage their business. They are a transportation providers for people who have Medicaid but do not have their one transportation. A few months ago we planned to hire one of our regular transportees (we have a fleet of vehicles that our drivers use). She seemed super nice, somewhat elderly, and just down on her luck. We ran her background check and it came back with wet horrible things on it. When we told her that she could not work for us, she lost control. He has accused my 80 year old grandfather of sexual abusing her (a man who I have never seen lose his temper or even yell). Put horrible rumors about him and my grandmother into people's heads. She has called the parent company we work under and told them that he beats her and has called the local hospital and impersonated the said parent company telling them my grandfather is banned from the er until said problems were solved. I want to hurt her for hurting my grnadparents. She has made horrible accusations about me abusing my child and terrible, horrible nasty things. I don't know what to do I'm at my absolute wits end with her!!