From my experience, there are a lot of bad people out there. For s/o like this, the best thing is not to give her an audience. She needs help and unless you’re a mental health prof. you can’t give it to her.
I never was really upset with my ex speaking bad about me, I understood why she was doing it. On the other hand, the people who spoke bad about me to her and convinced her to divorce me, are evil and insane. I’m sure they had/have sick mental reasons why they do/did it and it has nothing to do with me. These people will never have a cure to their sickness!