What do about friend drama?

When friends start drama over other friends, what are you suppose to do? One of my friends(friend A) just lost her best friend, and always talks about her to me. Me personally I hate listening to it.. I don’t like talking about my best friends behind their backs. Friend A will always say how my other friends are such bad friends, and there fake, and have terrible personality’s. And the people friend A is talking about are my best friends since kindergarten! I can’t listen to it anymore, and when I stick up for my best friends friend A argues with me saying how she knows I know shes right. But I just lost one of my friends, and now I keep my friends really close to me, my best friends are obviously closer to me than friend A. What should I say to friend A? I’m just out of ideas . Thank you very much :)