I am going to try to explain this with as little backstory as possible. Basically, I have a friend (J), who hates a girl (we'll call her A) that a few of our other friends are now friends with. She has very valid reasons, the girl is just a really bad person, our other friends used to agree, now suddenly a couple of them just love her.
A few weeks ago we all went out, and then a few people came back to my house. J had left and went somewhere else, we were supposed to call her later to let her know where we were. Other friends randomly invited A (without telling me until she showed up) then proceeded to talk some crap about J and how no one could tell her that they invited A because J would throw a fit. I went to bed within 5 minutes of this all because it just made me very uncomfortable. No one ever called J to come over (which was no big deal because she was with some other friends).
I hung out with J tonight, and in the conversation accidently said something about seeing A. She knows I'm not friends with her, so she asked me about it. I wasn't going to lie, so I told her. She is a little upset that she feels like these girls are lying to her (I did not tell her about the trash talking, just that they invited this girl over on a night when we were hanging out with her).
She handled it pretty well but her feelings are hurt, I'm not sure if she is going to say anything to these girls. Should I warn these girls that she is upset or just stay out of it?
Sorry I know some of this is vague, just trying to keep it brief.