What should I do?

Ok, so I have recently been questioning my friendship with a girl in my cl for the last couple of weeks. We are not that close, but she sits on my table in form and is quite good friends with my best friend and is in quite a few of my cles so we end up hanging out a lot. Another of my friends called Ami has been having problems lately and is really depressed and feels that some people hate her (but that is a different story).Anyway, Ami wrote this list of people that she think hate her and she highlighted some names and these were meant to show sluts (these girs had been spreadng rumours about her).Anyway she had written some people on there that Mel hangs out with that were sluts and Ami showed this list to one of her own good friends. But Mel was walking ped and snatched the list out of her hand. Then she started to talk about Ami quite rudely in front ofher, and I asked Mel not to tell her other friends as Ami already has enough stuff to deal with. Mel promised she