How to deal with an 87yo grandma that talks about things that never happened?

I'll try to make this post short. My 87yo grandma accused my dad of pointing a gun at her head and trying to kill her she says the police is already aware that he wants to take all her money and belongings, however, this never happened. We don't have guns in the house and my dad never ever did such thing we tried telling her this never happened she insists it did. My dad is devastated. She started making up similar stories too and my family doesn't know what to do. I live abroad and I also feel lost and shocked with what's going on.

How to deal with an 87yo grandma that talks about things that never happened?
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